build: removed -fcf-protection build option for old GCC

This allows oneDNN to build successfully with GCC 7.x

Author: vpirogov

cmake/SDL.cmake

@@ -30,9 +30,10 @@ macro(sdl_unix_common_ccxx_flags var)
     append(${var} "-fPIC -Wformat -Wformat-security")
 endmacro()
 
-macro(sdl_gnu_common_ccxx_flags var)
+macro(sdl_gnu_common_ccxx_flags var gnu_version)
     append(${var} "-fstack-protector-strong")
-    if(DNNL_TARGET_ARCH STREQUAL "X64")
+    if(NOT (${gnu_version} VERSION_LESS 8.0) 
+       AND (DNNL_TARGET_ARCH STREQUAL "X64"))
         append(${var} "-fcf-protection=full")
     endif()
 endmacro()
@@ -61,7 +62,8 @@ if(UNIX)
         append(ONEDNN_SDL_COMPILER_FLAGS "-D_FORTIFY_SOURCE=2")
     endif()
     if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-        sdl_gnu_common_ccxx_flags(ONEDNN_SDL_COMPILER_FLAGS)
+        sdl_gnu_common_ccxx_flags(ONEDNN_SDL_COMPILER_FLAGS
+                                  CMAKE_CXX_COMPILER_VERSION)
         sdl_gnu_src_ccxx_flags(CMAKE_SRC_CCXX_FLAGS)
         sdl_gnu_example_ccxx_flags(CMAKE_EXAMPLE_CCXX_FLAGS)
     elseif(CMAKE_CXX_COMPILER_ID MATCHES "(Apple)?[Cc]lang")