llvm-rc: Forward DEFINES instead of FLAGS

Since commit 1c2d031cbd (Add -E cmake_llvm_rc to preprocess files for
llvm-rc, 2020-01-14, v3.17.0-rc1~24^2) we pass the full target `<FLAGS>`
to the llvm-rc resource compiler, but we should pass only `<DEFINES>`.

Fixes: #20414

Modules/Platform/Windows-Clang.cmake

@@ -141,7 +141,7 @@ if("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC"
         set(CMAKE_RC_PREPROCESSOR CMAKE_CXX_COMPILER)
       endif()
       if(DEFINED CMAKE_RC_PREPROCESSOR)
-        set(CMAKE_RC_COMPILE_OBJECT "${CMAKE_COMMAND} -E cmake_llvm_rc <OBJECT>.pp <${CMAKE_RC_PREPROCESSOR}> <DEFINES> -DRC_INVOKED <INCLUDES> <FLAGS> -clang:-MD -clang:-MF -clang:<SOURCE>.d -E <SOURCE> -- <CMAKE_RC_COMPILER> <FLAGS> /fo <OBJECT> <OBJECT>.pp")
+        set(CMAKE_RC_COMPILE_OBJECT "${CMAKE_COMMAND} -E cmake_llvm_rc <OBJECT>.pp <${CMAKE_RC_PREPROCESSOR}> <DEFINES> -DRC_INVOKED <INCLUDES> <FLAGS> -clang:-MD -clang:-MF -clang:<SOURCE>.d -E <SOURCE> -- <CMAKE_RC_COMPILER> <DEFINES> /fo <OBJECT> <OBJECT>.pp")
         if(CMAKE_GENERATOR STREQUAL "Ninja")
           set(CMAKE_NINJA_CMCLDEPS_RC 0)
           set(CMAKE_NINJA_DEP_TYPE_RC gcc)