[cfe][CMake] Export the clang resource directory

[philip.pfaffe]

Summary

Out-of-tree tools trying to parse source files need the builtin headers
such as stddef.h. If the tool isn't installed together with clang, it
can't find them automatically. Exporting the location makes this much
easier.

[philip.pfaffe]

Abandoning in favor D49486, which subscribed the right list :)

clang/cmake/modules/CMakeLists.txt

 # Generate ClangConfig.cmake for the build tree.
 set(CLANG_CONFIG_CMAKE_DIR "${clang_cmake_builddir}")
 set(CLANG_CONFIG_LLVM_CMAKE_DIR "${llvm_cmake_builddir}")
 set(CLANG_CONFIG_EXPORTS_FILE "${clang_cmake_builddir}/ClangTargets.cmake")
 set(CLANG_CONFIG_INCLUDE_DIRS
   "${CLANG_SOURCE_DIR}/include"
   "${CLANG_BINARY_DIR}/include"
   )
+if (CLANG_RESOURCE_DIR)
+  set(CLANG_CONFIG_RESOURCE_DIR ${CLANG_RESOURCE_DIR})
+else()
+  set(CLANG_CONFIG_RESOURCE_DIR
+    ${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}/include)
+endif()
+
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/ClangConfig.cmake.in
   ${clang_cmake_builddir}/ClangConfig.cmake
   @ONLY)
 set(CLANG_CONFIG_CMAKE_DIR)
 set(CLANG_CONFIG_LLVM_CMAKE_DIR)
 set(CLANG_CONFIG_EXPORTS_FILE)
 

clang/cmake/modules/ClangConfig.cmake.in

 # This file allows users to call find_package(Clang) and pick up our targets.
 
 @CLANG_CONFIG_CODE@
 
 find_package(LLVM REQUIRED CONFIG
              HINTS "@CLANG_CONFIG_LLVM_CMAKE_DIR@")
 
 set(CLANG_EXPORTED_TARGETS "@CLANG_EXPORTS@")
 set(CLANG_CMAKE_DIR "@CLANG_CONFIG_CMAKE_DIR@")
 set(CLANG_INCLUDE_DIRS "@CLANG_CONFIG_INCLUDE_DIRS@")
+set(CLANG_RESOURCE_DIR "@CLANG_CONFIG_RESOURCE_DIR@")
 
 # Provide all our library targets to users.
 include("@CLANG_CONFIG_EXPORTS_FILE@")
 
 # By creating clang-tablegen-targets here, subprojects that depend on Clang's
 # tablegen-generated headers can always depend on this target whether building
 # in-tree with Clang or not.
 if(NOT TARGET clang-tablegen-targets)
   add_custom_target(clang-tablegen-targets)
 endif()