cmd/cgo: support clang on Windows

What version of Go are you using (go version)?

go version devel +0cff219 Wed Sep 7 10:43:13 2016 +0000 windows/amd64

What operating system and processor architecture are you using (go env)?

Windows 10 / AMD64

What did you do?

I used CGO with Clang for Windows 3.8.1 (http://llvm.org/releases/3.8.1/LLVM-3.8.1-win64.exe) like this:

set CC=clang set CGO_CFLAGS="-m64 -Ipath/to/my/includes" set CGO_LDFLAGS = "-v -Xlinker -libpath:path/to/libs -lwldap32 -ladvapi32 -lws2_32 -ldbghelp -luser32"

go build

What did you expect to see?

Expected to see nothing (ie, successful compile)

What did you see instead?

# editor/dom
clang version 3.8.1 (branches/release_38)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
 "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64\\link.exe" "-out:C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\_cgo_.o" -defaultlib:libcmt "-libpath:C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\lib\\amd64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\10\\Lib\\10.0.10240.0\\ucrt\\x64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\8.1\\Lib\\winv6.3\\um\\x64" -nologo "C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\_cgo_main.o" "C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\_cgo_export.o" "C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\binding.cgo2.o" "-libpath:c:\\temp\\go\\src\\editor\\.mm\\windows\\amd64\\release\\lib" core-static.lib ssl-static.lib crypto-static.lib ssh2-static.lib c-ares-static.lib user32.lib ws2_32.lib wldap32.lib advapi32.lib dbghelp.lib
   Creating library $WORK\editor\dom\_obj\_cgo_.lib and object $WORK\editor\dom\_obj\_cgo_.exp
core-static.lib(node.obj) : warning LNK4049: locally defined symbol xmlFree imported
core-static.lib(xml.obj) : warning LNK4049: locally defined symbol xmlFree imported
# editor/dom
clang version 3.8.1 (branches/release_38)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
 "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64\\link.exe" "-out:C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\_all.o" "-libpath:C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\lib\\amd64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\10\\Lib\\10.0.10240.0\\ucrt\\x64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\8.1\\Lib\\winv6.3\\um\\x64" -nologo "C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\_cgo_export.o" "C:\\Users\\CHRIST~1\\AppData\\Local\\Temp\\go-build406860094\\editor\\dom\\_obj\\binding.cgo2.o" -Wl,-r
LINK : warning LNK4044: unrecognized option '/Wl,-r'; ignored
LINK : fatal error LNK1561: entry point must be defined
clang.exe: error: linker command failed with exit code 1561 (use -v to see invocation)