standalone: use GCC_VERSION defined in compiler-gcc.h

Now GCC_VERSION is defined in include/linux/compiler-gcc.h
(with a little different definition).
Use it and delete the one in examples/standlone/stub.c.

This should work on Clang too because __GNUC__, __GNUC_MINOR__,
__GNUC_PATCHLEVEL__ are also defined on Clang.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jeroen Hofstee <jeroen@myspectrum.nl>

examples/standalone/stubs.c

@@ -1,9 +1,6 @@
 #include <common.h>
 #include <exports.h>
-
-#ifndef GCC_VERSION
-#define GCC_VERSION (__GNUC__ * 1000 + __GNUC_MINOR__)
-#endif /* GCC_VERSION */
+#include <linux/compiler.h>
 
 #if defined(CONFIG_X86)
 /*
@@ -237,7 +234,7 @@ gd_t *global_data;
  * implementation. On the other hand, asm() statements with
  * arguments can be used only inside the functions (gcc limitation)
  */
-#if GCC_VERSION < 3004
+#if GCC_VERSION < 30400
 static
 #endif /* GCC_VERSION */
 void __attribute__((unused)) dummy(void)