Linker error when compiling on windows

Hi,

Just as a preface, this issue might be related to #326 and #265

So when I compile a go script using the portaudio library, `ld` is able to find the portaudio.dll. In the same way, when compiling `ui` code, go is able to compile it. However, when I try to compile portaudio and ui code, `ld` is not able to find the portaudio dll.

After checking the verbose output, the difference is that when it does not work, g++ is used instead of gcc when calling the external linker.

What I don't understand is that when calling `ld` from the command line with the `-L` flag to specify the linker library, it is able to find the portaudio dll, But when compiling with go build, the linker is not able to find the dll and it is confusing the hell out of me haha.

For reference, this is the failed build script:

```
WORK=C:\Users\nadav\AppData\Local\Temp\go-build899281014
mkdir -p $WORK\b001\
cat >$WORK\b001\importcfg.link << 'EOF' # internal
packagefile command-line-arguments=C:\Users\nadav\AppData\Local\go-build\82\824845ce2bbcbae9b36bc0262184eb3f4721048c3da4ed0f1adf54d458d910c7-d
packagefile github.com/andlabs/ui=C:\Users\nadav\go\pkg\windows_amd64\github.com\andlabs\ui.a
packagefile github.com/andlabs/ui/winmanifest=C:\Users\nadav\go\pkg\windows_amd64\github.com\andlabs\ui\winmanifest.a
packagefile github.com/gordonklaus/portaudio=C:\Users\nadav\go\pkg\windows_amd64\github.com\gordonklaus\portaudio.a
packagefile runtime=c:\go\pkg\windows_amd64\runtime.a
packagefile errors=c:\go\pkg\windows_amd64\errors.a
packagefile image=c:\go\pkg\windows_amd64\image.a
packagefile sync=c:\go\pkg\windows_amd64\sync.a
packagefile time=c:\go\pkg\windows_amd64\time.a
packagefile runtime/cgo=c:\go\pkg\windows_amd64\runtime\cgo.a
packagefile syscall=c:\go\pkg\windows_amd64\syscall.a
packagefile fmt=c:\go\pkg\windows_amd64\fmt.a
packagefile os=c:\go\pkg\windows_amd64\os.a
packagefile reflect=c:\go\pkg\windows_amd64\reflect.a
packagefile internal/bytealg=c:\go\pkg\windows_amd64\internal\bytealg.a
packagefile internal/cpu=c:\go\pkg\windows_amd64\internal\cpu.a
packagefile runtime/internal/atomic=c:\go\pkg\windows_amd64\runtime\internal\atomic.a
packagefile runtime/internal/math=c:\go\pkg\windows_amd64\runtime\internal\math.a
packagefile runtime/internal/sys=c:\go\pkg\windows_amd64\runtime\internal\sys.a
packagefile internal/reflectlite=c:\go\pkg\windows_amd64\internal\reflectlite.a
packagefile bufio=c:\go\pkg\windows_amd64\bufio.a
packagefile image/color=c:\go\pkg\windows_amd64\image\color.a
packagefile io=c:\go\pkg\windows_amd64\io.a
packagefile strconv=c:\go\pkg\windows_amd64\strconv.a
packagefile sync/atomic=c:\go\pkg\windows_amd64\sync\atomic.a
packagefile internal/race=c:\go\pkg\windows_amd64\internal\race.a
packagefile internal/syscall/windows/registry=c:\go\pkg\windows_amd64\internal\syscall\windows\registry.a
packagefile internal/oserror=c:\go\pkg\windows_amd64\internal\oserror.a
packagefile internal/syscall/windows/sysdll=c:\go\pkg\windows_amd64\internal\syscall\windows\sysdll.a
packagefile unicode/utf16=c:\go\pkg\windows_amd64\unicode\utf16.a
packagefile internal/fmtsort=c:\go\pkg\windows_amd64\internal\fmtsort.a
packagefile math=c:\go\pkg\windows_amd64\math.a
packagefile unicode/utf8=c:\go\pkg\windows_amd64\unicode\utf8.a
packagefile internal/poll=c:\go\pkg\windows_amd64\internal\poll.a
packagefile internal/syscall/windows=c:\go\pkg\windows_amd64\internal\syscall\windows.a
packagefile internal/testlog=c:\go\pkg\windows_amd64\internal\testlog.a
packagefile unicode=c:\go\pkg\windows_amd64\unicode.a
packagefile bytes=c:\go\pkg\windows_amd64\bytes.a
packagefile math/bits=c:\go\pkg\windows_amd64\math\bits.a
packagefile sort=c:\go\pkg\windows_amd64\sort.a
EOF
mkdir -p $WORK\b001\exe\
cd .
"c:\\go\\pkg\\tool\\windows_amd64\\link.exe" -o "C:\\Users\\nadav\\AppData\\Local\\Temp\\go-build899281014\\b001\\exe\\a.out.exe" -importcfg "C:\\Users\\nadav\\AppData\\Local\\Temp\\go-build899281014\\b001\\importcfg.link" -buildmode=exe -buildid=qbWb98bCfThjdneEe-oJ/fi_1RHQuG_COvVrnh5VK/Yvcj_mZYbyoyFkQvTr_g/qbWb98bCfThjdneEe-oJ -extldflags "-LC:\\TDM-GCC-64\\lib\\ --verbose" -extld=g++ "C:\\Users\\nadav\\AppData\\Local\\go-build\\82\\824845ce2bbcbae9b36bc0262184eb3f4721048c3da4ed0f1adf54d458d910c7-d"
# command-line-arguments
c:\go\pkg\tool\windows_amd64\link.exe: running g++ failed: exit status 1
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/9.2.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../../../src/gcc-git-9.2.0/configure --build=x86_64-w64-mingw32 --enable-targets=all --enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-libgomp --enable-lto --enable-graphite --enable-cxx-flags=-DWINPTHREAD_STATIC --disable-build-with-cxx --disable-build-poststage1-with-cxx --enable-libstdcxx-debug --enable-threads=posix --enable-version-specific-runtime-libs --enable-fully-dynamic-string --enable-libstdcxx-threads --enable-libstdcxx-time --with-gnu-ld --disable-werror --disable-nls --disable-win32-registry --enable-large-address-aware --disable-rpath --disable-symvers --prefix=/mingw64tdm --with-local-prefix=/mingw64tdm --with-pkgversion=tdm64-1 --with-bugurl=http://tdm-gcc.tdragon.net/bugs
Thread model: posix
gcc version 9.2.0 (tdm64-1)
COMPILER_PATH=C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/9.2.0/;C:/TDM-GCC-64/bin/../libexec/gcc/;C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/
LIBRARY_PATH=C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/;C:/TDM-GCC-64/bin/../lib/gcc/;C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib/../lib/;C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../lib/;C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib/;C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../
COLLECT_GCC_OPTIONS='-m64' '-mconsole' '-o' 'C:\Users\nadav\AppData\Local\Temp\go-build899281014\b001\exe\a.out.exe' '-g' '-O2' '-static' '-static-libgcc' '-g' '-O2' '-LC:/MinGW/msys/1.0/local/lib' '-g' '-O2' '-no-pie' '-LC:\TDM-GCC-64\lib\' '-v' '-mtune=generic' '-march=x86-64'
C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/9.2.0/collect2.exe -plugin C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/9.2.0/liblto_plugin-0.dll -plugin-opt=C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/9.2.0/lto-wrapper.exe -plugin-opt=-fresolution=C:\Users\nadav\AppData\Local\Temp\cceGIZXB.res -plugin-opt=-pass-through=-lmingw32 -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lmoldname -plugin-opt=-pass-through=-lmingwex -plugin-opt=-pass-through=-lmsvcrt -plugin-opt=-pass-through=-lpthread -plugin-opt=-pass-through=-ladvapi32 -plugin-opt=-pass-through=-lshell32 -plugin-opt=-pass-through=-luser32 -plugin-opt=-pass-through=-lkernel32 -plugin-opt=-pass-through=-lmingw32 -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lmoldname -plugin-opt=-pass-through=-lmingwex -plugin-opt=-pass-through=-lmsvcrt -m i386pep --exclude-libs=libpthread.a --subsystem console -Bstatic -o $WORK\b001\exe\a.out.exe C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib/../lib/crt2.o C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/crtbegin.o -LC:/MinGW/msys/1.0/local/lib -LC:\TDM-GCC-64\lib\ -LC:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0 -LC:/TDM-GCC-64/bin/../lib/gcc -LC:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib/../lib -LC:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../lib -LC:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib -LC:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../.. C:\Users\nadav\AppData\Local\Temp\go-link-100908443\go.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000000.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000001.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000002.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000003.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000004.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000005.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000006.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000007.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000008.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000009.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000010.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000011.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000012.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000013.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000014.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000015.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000016.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000017.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000018.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000019.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000020.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000021.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000022.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000023.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000024.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000025.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000026.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000027.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000028.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000029.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000030.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000031.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000032.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000033.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000034.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000035.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000036.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000037.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000038.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000039.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000040.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000041.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000042.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000043.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000044.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000045.o C:\Users\nadav\AppData\Local\Temp\go-link-100908443\000046.o C:/Users/nadav/go/src/github.com/andlabs/ui/libui_windows_amd64.a -luser32 -lkernel32 -lgdi32 -lcomctl32 -luxtheme -lmsimg32 -lcomdlg32 -ld2d1 -ldwrite -lole32 -loleaut32 -loleacc -luuid -lwindowscodecs -lportaudio -lwinmm -lm -lole32 -luuid -T C:\Users\nadav\AppData\Local\Temp\go-link-100908443\fix_debug_gdb_scripts.ld --start-group -lmingwex -lmingw32 --end-group -lkernel32 -lstdc++ -lmingw32 -lgcc -lmoldname -lmingwex -lmsvcrt -lpthread -ladvapi32 -lshell32 -luser32 -lkernel32 -lmingw32 -lgcc -lmoldname -lmingwex -lmsvcrt C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/lib/../lib/default-manifest.o C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/crtend.o
C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lportaudio
collect2.exe: error: ld returned 1 exit status
```

#### Go Env
```
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\nadav\AppData\Local\go-build
set GOENV=C:\Users\nadav\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\nadav\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\nadav\AppData\Local\Temp\go-build214969006=/tmp/go-build -gno-record-gcc-switches
```

For reference, I am using the TDM-GCC compiler