CMake: Only pass -fno-rtti and -frtti for C++ targets

dtool/CompilerFlags.cmake

@@ -190,8 +190,8 @@ else()
 
   check_cxx_compiler_flag("-fno-rtti" COMPILER_SUPPORTS_FRTTI)
   if(COMPILER_SUPPORTS_FRTTI)
-    set(cxx_rtti_on "-frtti")
-    set(cxx_rtti_off "-fno-rtti")
+    set(cxx_rtti_on "$<$<OR:$<COMPILE_LANGUAGE:CXX>,$<COMPILE_LANGUAGE:OBJCXX>>:-frtti>")
+    set(cxx_rtti_off "$<$<OR:$<COMPILE_LANGUAGE:CXX>,$<COMPILE_LANGUAGE:OBJCXX>>:-fno-rtti>")
 
   else()
     set(cxx_rtti_on)