Consistently set and use CLANG_CMAKE_DIR

For standard CMake, Clang_DIR should include the lib/cmake/clang
subdirectory suffix. This currently works only because Clad defines
HINTS itself.

CMakeLists.txt

@@ -23,7 +23,7 @@ if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
 
   find_package(Clang REQUIRED CONFIG)
   message(STATUS "Found supported version: Clang ${CLANG_PACKAGE_VERSION}")
-  message(STATUS "Using ClangConfig.cmake in: ${Clang_DIR}")
+  message(STATUS "Using ClangConfig.cmake in: ${CLANG_CMAKE_DIR}")
 
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
@@ -111,6 +111,7 @@ else()
     list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
     include(${LLVMCONFIG_FILE})
   endif()
+  set(CLANG_CMAKE_DIR "${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/clang")
   if (NOT CLANG_INCLUDE_DIRS)
     set (CLANG_INCLUDE_DIRS "${LLVM_MAIN_SRC_DIR}/tools/clang/include")
     if (NOT EXISTS ${CLANG_INCLUDE_DIRS})

cmake/modules/CMakeLists.txt

@@ -13,7 +13,7 @@ export(TARGETS ${CLING_EXPORTS} FILE ${cling_cmake_builddir}/ClingTargets.cmake)
 
 # Generate ClingConfig.cmake for the build tree.
 set(CLING_CONFIG_CMAKE_DIR "${cling_cmake_builddir}")
-set(CLING_CONFIG_CLANG_CMAKE_DIR "${clang_cmake_builddir}")
+set(CLING_CONFIG_CLANG_CMAKE_DIR "${CLANG_CMAKE_DIR}")
 set(CLING_CONFIG_EXPORTS_FILE "${cling_cmake_builddir}/ClingTargets.cmake")
 set(CLING_CONFIG_INCLUDE_DIRS
   "${CLING_SOURCE_DIR}/include"

tools/plugins/clad/CMakeLists.txt

@@ -46,10 +46,6 @@ if (CMAKE_CXX_STANDARD)
   list(APPEND _clad_extra_cmake_args -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD})
 endif(CMAKE_CXX_STANDARD)
 
-if (Clang_DIR)
-  list(APPEND _clad_extra_cmake_args -DClang_DIR=${Clang_DIR} -DClang_CONFIG_EXTRA_PATH_HINTS=${Clang_Config_ExtraPathHints})
-endif(Clang_DIR)
-
 if (LLVM_FORCE_USE_OLD_TOOLCHAIN)
   list(APPEND _clad_extra_cmake_args -DLLVM_FORCE_USE_OLD_TOOLCHAIN=${LLVM_FORCE_USE_OLD_TOOLCHAIN})
 endif(LLVM_FORCE_USE_OLD_TOOLCHAIN)
@@ -94,7 +90,7 @@ ExternalProject_Add(
              -DCMAKE_CXX_FLAGS=${CLAD_CXX_FLAGS}
              -DCMAKE_INSTALL_PREFIX=${clad_install_dir}/plugins
              -DLLVM_DIR=${LLVM_BINARY_DIR}
-             -DCLANG_INCLUDE_DIRS=${CLANG_INCLUDE_DIRS}
+             -DClang_DIR=${CLANG_CMAKE_DIR}
              ${_clad_extra_cmake_args}
   # FIXME
   # Building with 1 core is a temporary workaround for #16654 and has to be