[CMake] Store path to vendor-specific headers in clang-headers target property

[sgraenitz]

Summary

LLDB.framework wants a copy these headers. With this change LLDB can easily glob for the list of files:

get_target_property(clang_include_dir clang-headers RUNTIME_OUTPUT_DIRECTORY)
file(GLOB_RECURSE clang_vendor_headers RELATIVE ${clang_include_dir} "${clang_include_dir}/*")

By default RUNTIME_OUTPUT_DIRECTORY is unset for custom targets like clang-headers.
Not sure if there is a read&write property that matches the purpose better.

What do you think?

[JDevlieghere]

This makes sense to me. I'm don't know if there's a better property but I think this matches the intended use, so I think it is fine.

cfe/trunk/lib/Headers/CMakeLists.txt

foreach( f ${files} ${cuda_wrapper_files} )
   set( dst ${output_dir}/${f} )
   add_custom_command(OUTPUT ${dst}
     DEPENDS ${src}
     COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
     COMMENT "Copying clang's ${f}...")
   list(APPEND out_files ${dst})
 endforeach( f )
 
-add_custom_command(OUTPUT ${output_dir}/arm_neon.h 
+add_custom_command(OUTPUT ${output_dir}/arm_neon.h
   DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/arm_neon.h
   COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/arm_neon.h ${output_dir}/arm_neon.h
   COMMENT "Copying clang's arm_neon.h...")
 list(APPEND out_files ${output_dir}/arm_neon.h)
 add_custom_command(OUTPUT ${output_dir}/arm_fp16.h
   DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/arm_fp16.h
   COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/arm_fp16.h ${output_dir}/arm_fp16.h
   COMMENT "Copying clang's arm_fp16.h...")
 list(APPEND out_files ${output_dir}/arm_fp16.h)
 
 add_custom_target(clang-headers ALL DEPENDS ${out_files})
-set_target_properties(clang-headers PROPERTIES FOLDER "Misc")
+set_target_properties(clang-headers PROPERTIES
+  FOLDER "Misc"
+  RUNTIME_OUTPUT_DIRECTORY "${output_dir}")
 
 install(
   FILES ${files} ${CMAKE_CURRENT_BINARY_DIR}/arm_neon.h
   COMPONENT clang-headers
   PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
   DESTINATION lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}/include)
 
 install(