[MinGW] Look for libc++ headers in a triplet prefixed path as well

[mstorsjo]

Summary

This makes it consistent with libstdc++ and the other default include directories.

If these headers are found in both locations and one isn't a symlink to the other, this will cause errors due to libc++ headers having wrapper headers for some standard C headers, wrappers that do #include_next the actual one.

If the same libc++ standard C wrapper header exists in more than one include directory before the real system one, the header include guard will stop it from doing another #include_next to pick up the real one, breaking things.

As this is a rather uncommon situation, this should be acceptable and toolchain maintainers can adapt accordingly if necessary.

[rnk]

lgtm

lib/Driver/ToolChains/MinGW.cpp

463

Holy cow, this is long. =/ Maybe make a local variable Slash and use it?

[mstorsjo]

lib/Driver/ToolChains/MinGW.cpp

463

Ok, will do before pushing.

lib/Driver/ToolChains/MinGW.cpp

 }
 
 void toolchains::MinGW::AddClangCXXStdlibIncludeArgs(
     const ArgList &DriverArgs, ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
       DriverArgs.hasArg(options::OPT_nostdincxx))
     return;
 
+  StringRef Slash = llvm::sys::path::get_separator();
+
   switch (GetCXXStdlibType(DriverArgs)) {
   case ToolChain::CST_Libcxx:
+    addSystemInclude(DriverArgs, CC1Args, Base + Arch + Slash + "include" +
+                                              Slash + "c++" + Slash + "v1");
     addSystemInclude(DriverArgs, CC1Args,
-                     Base + "include" + llvm::sys::path::get_separator() +
-                         "c++" + llvm::sys::path::get_separator() + "v1");
+                     Base + "include" + Slash + "c++" + Slash + "v1");
     break;
 
   case ToolChain::CST_Libstdcxx:
     llvm::SmallVector<llvm::SmallString<1024>, 4> CppIncludeBases;
     CppIncludeBases.emplace_back(Base);
     llvm::sys::path::append(CppIncludeBases[0], Arch, "include", "c++");
     CppIncludeBases.emplace_back(Base);
     llvm::sys::path::append(CppIncludeBases[1], Arch, "include", "c++", Ver);
     CppIncludeBases.emplace_back(Base);
     llvm::sys::path::append(CppIncludeBases[2], "include", "c++", Ver);
     CppIncludeBases.emplace_back(GccLibDir);
     llvm::sys::path::append(CppIncludeBases[3], "include", "c++");
     for (auto &CppIncludeBase : CppIncludeBases) {
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase);
-      CppIncludeBase += llvm::sys::path::get_separator();
+      CppIncludeBase += Slash;
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + Arch);
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + "backward");
     }
     break;
   }
 }

test/Driver/mingw.cpp

 // RUN: %clang -target i686-windows-gnu -rtlib=platform -c -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_CLANG_TREE %s
 // CHECK_MINGW_CLANG_TREE: "{{.*}}/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"
 // CHECK_MINGW_CLANG_TREE: "{{.*}}/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}include"
 
 
+// RUN: %clang -target i686-windows-gnu -rtlib=platform -stdlib=libc++ -c -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_CLANG_TREE_LIBCXX %s
+// CHECK_MINGW_CLANG_TREE_LIBCXX: "{{.*}}/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}v1"
+
+
 // RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_mingw_org_tree/mingw %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ORG_TREE %s
 // CHECK_MINGW_ORG_TREE: "{{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_MINGW_ORG_TREE: "{{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}mingw32"
 // CHECK_MINGW_ORG_TREE: "{{.*}}{{/|\\\\}}Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
 // CHECK_MINGW_ORG_TREE: "{{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}mingw32{{/|\\\\}}include"
 // CHECK_MINGW_ORG_TREE: {{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}include