[CMake] install clang and other resource headers into `CLANG_RESOURCE_DIR/include` if `CLANG_RESOURCE_DIR` is not empty

[paperchalice]

Summary

When CLANG_RESOURCE_DIR is not empty, clang will look up builtin headers in CLANG_RESOURCE_DIR/include, this patch makes sure resource headers are installed into the correct location.
Resolve issue #57708.

[phosek]

clang/lib/Headers/CMakeLists.txt

266

The property we maintain is that the build directory layout matches the installation directory which makes it possible to use the toolchain without having to install it first.

I believe we need to set the output_dir depending on the value of CLANG_RESOURCE_DIR as well to preserve that behavior.

423–426

nit: can we use if ... else?

[paperchalice]

Update the output_dir.

[phosek]

LGTM

[paperchalice]

If it is ready to land, could you commit this change? I don't have commit right, thanks.

[paperchalice]

Let other projects consider CLANG_RESOURCE_DIR too.

[paperchalice]

Ping @phosek, but may need suggestions from other reviewers...
Thanks in advance if someone can commit this change.

openmp/CMakeLists.txt

80 ↗

(On Diff #466249)

Should support CLANG_RESOURCE_DIR in standalone mode?

clang/lib/Headers/CMakeLists.txt

set(openmp_wrapper_files
   openmp_wrappers/cmath
   openmp_wrappers/complex.h
   openmp_wrappers/complex
   openmp_wrappers/__clang_openmp_device_functions.h
   openmp_wrappers/complex_cmath.h
   openmp_wrappers/new
 )
 
 set(output_dir ${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}/include)
 set(out_files)
 set(generated_files)
 
 set(arm_common_generated_files)
 set(arm_only_generated_files)
 set(aarch64_only_generated_files)
 set(riscv_generated_files)
 

 
 # Other header groupings
 add_header_target("hlsl-resource-headers" ${hlsl_files})
 add_header_target("opencl-resource-headers" ${opencl_files})
 add_header_target("openmp-resource-headers" ${openmp_wrapper_files})
 add_header_target("windows-resource-headers" ${windows_only_files})
 add_header_target("utility-resource-headers" ${utility_files})
 
 set(header_install_dir lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}/include)
+if(NOT CLANG_RESOURCE_DIR STREQUAL "")
+  set(header_install_dir ${CMAKE_INSTALL_BINDIR}/${CLANG_RESOURCE_DIR}/include)
+endif()
 
 #############################################################
 # Install rules for the catch-all clang-resource-headers target
 install(
   FILES ${files} ${generated_files}
   DESTINATION ${header_install_dir}
   COMPONENT clang-resource-headers)