fortify: Replace open-coded __gnu_inline attribute

Replace open-coded gnu_inline attribute with the normal kernel
convention for attributes: __gnu_inline

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220208225350.1331628-2-keescook@chromium.org

Author: kees

include/linux/fortify-string.h

@@ -2,7 +2,7 @@
 #ifndef _LINUX_FORTIFY_STRING_H_
 #define _LINUX_FORTIFY_STRING_H_
 
-#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
+#define __FORTIFY_INLINE extern __always_inline __gnu_inline
 #define __RENAME(x) __asm__(#x)
 
 void fortify_panic(const char *name) __noreturn __cold;