append is not supported, return original code

Signed-off-by: Tikhomirova, Kseniya <kseniya.tikhomirova@intel.com>

Author: KseniyaTikhomirova

CMakeLists.txt

@@ -99,8 +99,8 @@ function(add_cxx_flag_if_supported flag)
     mangle_name("${flag}" flagname)
     check_cxx_compiler_flag("${flag}" "CXX_SUPPORTS_${flagname}_FLAG")
 	if (CXX_SUPPORTS_${flagname}_FLAG)
-		append("${flag}" CMAKE_CXX_FLAGS)
-		append("${flag}" CMAKE_C_FLAGS)
+		set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}")
+		set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${flag}")
 	endif()
 endfunction()