[TCP Tunnel] Failed to build the tcp-tnnnel binary

I added the "-v" flag when build the project.

```
➜ tcp-tunnel git:(master) ✗ make
Compiling from source...
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: aarch64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-ios5.0.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -faligned-alloc-unavailable -target-cpu cyclone -target-feature +fp-armv8 -target-feature +neon -target-feature +crypto -target-feature +zcm -target-feature +zcz -target-abi darwinpcs -fallow-half-arguments-and-returns -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -D OUT_OF_TREE_BUILD -I /Users/yly/Documents/iOS/xnu-qemu-arm64/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /Users/yly/Documents/iOS/xnu-qemu-arm64-tools/tcp-tunnel -ferror-limit 19 -fmessage-length 204 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=ios-5.0.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/main-19bc74.o -x c src/main.c
clang -cc1 version 10.0.1 (clang-1001.0.46.4) default target x86_64-apple-darwin18.7.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/Users/yly/Documents/iOS/xnu-qemu-arm64/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-ios5.0.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name fds.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -faligned-alloc-unavailable -target-cpu cyclone -target-feature +fp-armv8 -target-feature +neon -target-feature +crypto -target-feature +zcm -target-feature +zcz -target-abi darwinpcs -fallow-half-arguments-and-returns -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -D OUT_OF_TREE_BUILD -I /Users/yly/Documents/iOS/xnu-qemu-arm64/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /Users/yly/Documents/iOS/xnu-qemu-arm64-tools/tcp-tunnel -ferror-limit 19 -fmessage-length 204 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=ios-5.0.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/fds-b538ff.o -x c src/qemu-guest-services/fds.c
clang -cc1 version 10.0.1 (clang-1001.0.46.4) default target x86_64-apple-darwin18.7.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/Users/yly/Documents/iOS/xnu-qemu-arm64/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-ios5.0.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name general.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -faligned-alloc-unavailable -target-cpu cyclone -target-feature +fp-armv8 -target-feature +neon -target-feature +crypto -target-feature +zcm -target-feature +zcz -target-abi darwinpcs -fallow-half-arguments-and-returns -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -D OUT_OF_TREE_BUILD -I /Users/yly/Documents/iOS/xnu-qemu-arm64/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /Users/yly/Documents/iOS/xnu-qemu-arm64-tools/tcp-tunnel -ferror-limit 19 -fmessage-length 204 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=ios-5.0.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/general-752beb.o -x c src/qemu-guest-services/general.c
clang -cc1 version 10.0.1 (clang-1001.0.46.4) default target x86_64-apple-darwin18.7.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/Users/yly/Documents/iOS/xnu-qemu-arm64/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-ios5.0.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name socket.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -faligned-alloc-unavailable -target-cpu cyclone -target-feature +fp-armv8 -target-feature +neon -target-feature +crypto -target-feature +zcm -target-feature +zcz -target-abi darwinpcs -fallow-half-arguments-and-returns -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -D OUT_OF_TREE_BUILD -I /Users/yly/Documents/iOS/xnu-qemu-arm64/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /Users/yly/Documents/iOS/xnu-qemu-arm64-tools/tcp-tunnel -ferror-limit 19 -fmessage-length 204 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=ios-5.0.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/socket-4fdcaf.o -x c src/qemu-guest-services/socket.c
clang -cc1 version 10.0.1 (clang-1001.0.46.4) default target x86_64-apple-darwin18.7.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/Users/yly/Documents/iOS/xnu-qemu-arm64/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch arm64 -iphoneos_version_min 5.0.0 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -o bin/tunnel /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/main-19bc74.o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/fds-b538ff.o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/general-752beb.o /var/folders/g_/g3njrmcn76gc_606mkfgw9240000gn/T/socket-4fdcaf.o -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/lib/darwin/libclang_rt.ios.a
Undefined symbols for architecture arm64:
"start", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [bin/tunnel] Error 1
```