Fix destination for clang-builtin-headers-in-clang-resource-dir

`LLVM_LIBRARY_OUTPUT_INTDIR` already points to the `lib` subdirectory of
LLVM build folder.

Addresses rdar://70486284

Author: edymtt

stdlib/public/SwiftShims/CMakeLists.txt

@@ -223,8 +223,8 @@ endif()
 # need to use a different version of the headers than the installed Clang. This
 # should be used in conjunction with clang-resource-dir-symlink.
 file(TO_CMAKE_PATH "${LLVM_LIBRARY_OUTPUT_INTDIR}"
-  _SWIFT_SHIMS_PATH_TO_CLANG_BUILD)
-swift_install_in_component(DIRECTORY "${_SWIFT_SHIMS_PATH_TO_CLANG_BUILD}/lib/clang"
+  _SWIFT_SHIMS_PATH_TO_CLANG_LIB_BUILD)
+swift_install_in_component(DIRECTORY "${_SWIFT_SHIMS_PATH_TO_CLANG_LIB_BUILD}/clang"
                            DESTINATION "lib"
                            COMPONENT clang-builtin-headers-in-clang-resource-dir
                            PATTERN "*.h")