WIN64: 'undefined reference to `icudt62_dat`' error for builds using mingw-w64 with ICU

Hello everyone,

For builds using mingw-w64 got errors:
```
.\b2 --build-type=complete toolset=gcc-8.1.0 variant=release link=static threading=multi runtime-link=static address-model=64 -sICU_PATH="%CD%\..\..\libICU-63.1-dev\GCC64RT" -sICU_LINK="-L"%CD%\..\..\libICU-63.1-dev\GCC64RT\lib" -lsicuuc -lsicuin -lsicudt" -d2 -q
Performing configuration checks

- icu : no
- icu (lib64) : no

"g++" -m64 -O0 -fno-inline -Wall -g -DBOOST_ALL_NO_LIB=1 -I"." -I"c:\libICU-63.1-dev\GCC64RT\include" -c -o "bin.v2\libs\locale\build\gcc-8.1.0\debug\has_icu64_obj.o" "libs\locale\src\..\build\has_icu_test.cpp"

libs\locale\src\..\build\has_icu_test.cpp: In function 'int main()':
libs\locale\src\..\build\has_icu_test.cpp:26:12: warning: unused variable 'c' [-Wunused-variable]
UChar32 c = ::u_charFromName(U_UNICODE_CHAR_NAME, "GREEK SMALL LETTER ALPHA", &err);
^
gcc.link bin.v2\libs\locale\build\gcc-8.1.0\debug\has_icu64.exe

"g++" -Wl,-rpath -Wl,"c:\libICU-63.1-dev\GCC64RT\bin64" -o "bin.v2\libs\locale\build\gcc-8.1.0\debug\has_icu64.exe" -Wl,--start-group "bin.v2\libs\locale\build\gcc-8.1.0\debug\has_icu64_obj.o" -Wl,-Bstatic -Wl,-Bdynamic -Wl,--end-group -m64 -g -Lc:\libBOOST-1.68.0-dev\build\..\..\libICU-63.1-dev\GCC64RT\lib -lsicudt -lsicuin -lsicuuc

c:\libBOOST-1.68.0-dev\build\..\..\libICU-63.1-dev\GCC64RT\lib/libsicuuc.a(udata.ao):udata.cpp:(.rdata$.refptr.icudt62_dat[.refptr.icudt62_dat]+0x0): undefined reference to `icudt62_dat'
collect2.exe: error: ld returned 1 exit status
...failed gcc.link bin.v2\libs\locale\build\gcc-8.1.0\debug\has_icu64.exe...
...failed updating 1 target...
...updated 1 target...
...found 11 targets...
...updating 8 targets...
common.mkdir bin.v2\libs\log
```
during `libs\regex\build\has_icu_test.cpp` and `libs\locale\build\has_icu_test.cpp` build.

Reproduced for:
- builds using mingw-w64 with static ICU binaries,

not reproduced for:
- builds using mingw-w64 with shared ICU binaries,
- builds using Windows ICC and MSVC with static ICU binaries.

Environment:
- Windows 10 x64 10.0.17134.1,
- mingw-w64 x86_64 posix seh 8.1.0,
- ICC 2018 Update 3,
- MSVC 2017 15.7.3,
- Windows SDK 10.0.17134.12,
- Boost-1.68.0-dev-ddc1a4f91dd30a716384a5f85557101d7b45da85.

A source of error is improper library order in the linker command:
```
-lsicudt -lsicuin -lsicuuc
```
while expected to be:
```
-lsicuuc -lsicudt -lsicuin
```
as in `libs\locale\build\Jamfile.v2:121:14` or
```
-lsicuin -lsicuuc -lsicudt
```
as used during ICU tools and test-suite build.
ICU libraries order was set correctly in Boost configuration command (see above), but was changed by Boost build system (all `-l*` flags were set in alphabetical order). This have no effect for builds with shared ICU binaries but result to errors in case static binaries use.
MSVC linker is also sensitive to the libraries order in build command, but for some reason has no such errors in this case.

P.S. also drawing your attention, that `libs\regex\build\Jamfile.v2` and `libs\locale\build\Jamfile.v2` significantly differs, while relate to the same area (ICU support); presumably because 1st one wasn't covered with a commit like https://github.com/boostorg/locale/commit/1d7179612f4db1d27836577f690efe859e68a491 by @artyom-beilis.

Best,

Alexander