[tests][go]Add -stdlib=libc++ to build GO test if LLVM is built with libc++

[xingxue]

Summary

When libc++ is used to build LLVM libraries, these libraries have dependencies on libc++ and C++ STL signatures in these libraries are corresponding to libc++ implementation. Therefore, -stdlib=libc++ is required on the C++ compiler command for building GO tests that link with these LLVM libraries.

[sfertile]

LGTM.

[hubert.reinterpretcast]

llvm/tools/llvm-go/llvm-go.go

98

The added lines use spaces in place of the tabs used on the other lines.

[xingxue]

llvm/tools/llvm-go/llvm-go.go

98

Thanks for spotting this. Changed to use tabs.

llvm/tools/llvm-go/llvm-go.go

 func llvmFlags() compilerFlags {
   args := append([]string{"--ldflags", "--libs", "--system-libs"}, components...)
   ldflags := llvmConfig(args...)
+        stdLibOption := ""
+        if strings.Contains(llvmConfig("--cxxflags"), "-stdlib=libc++") {
+                // If libc++ is used to build LLVM libraries, -stdlib=libc++ is
+                // needed to resolve dependent symbols
+                stdLibOption = "-stdlib=libc++"
+        }
   if runtime.GOOS != "darwin" {
     // OS X doesn't like -rpath with cgo. See:
     // https://github.com/golang/go/issues/7293

   }
   return compilerFlags{
     cpp: llvmConfig("--cppflags"),
-    cxx: "-std=c++11",
+    cxx: "-std=c++11" + " " + stdLibOption,
     ld:  ldflags,
   }
 }