[llvm] Fix resource path when building tools

[JackBoosY]

Default resource directory for clang is constructed relative to the location of the clang executable:

From clang/lib/Driver/Driver.cpp:

std::string Driver::GetResourcesPath(StringRef BinaryPath,
                                     StringRef CustomResourceDir) {
...
  // Dir is bin/ or lib/, depending on where BinaryPath is.
  std::string Dir = llvm::sys::path::parent_path(BinaryPath);
...
    P = llvm::sys::path::parent_path(Dir);
    llvm::sys::path::append(P, Twine("lib") + CLANG_LIBDIR_SUFFIX, "clang",
                            CLANG_VERSION_STRING);
...
}

Vcpkg moves clang to tools/llvm adding a subdirectory. As a result the above code produces tools/lib/clang/11.0.0 which does not exist. Clang is therefore unable to find header files under lib/clang/11.0.0.

From clang/lib/Driver/ToolChains/Clang.cpp:

  // Pass the path to compiler resource files.
  CmdArgs.push_back("-resource-dir");
  CmdArgs.push_back(D.ResourceDir.c_str());

I have worked around the problem by adding this to my ports/llvm/portfile.cmake

list(APPEND FEATURE_OPTIONS
     -DCLANG_RESOURCE_DIR=../../lib/clang/11.0.0
)

Fix this.

Fixes #16284.

[JackBoosY]

Hi @mcurtis-cadence, does this changes meet your requirement?

[PhoebeHui]

cc @yurybura

[mcurtis-cadence]

@JackBoosY

does this changes meet your requirement?

Yes, that works for me.
Thanks!

[PhoebeHui]

LGTM, @strega-nil, could you help futher review?