setup attribute_optimize which comes with gcc-4.4+

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

include/libc-symbols.h

@@ -85,6 +85,12 @@
 # define __cast__(_to)
 #endif
 
+#if defined __GNUC__ && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4))
+# define attribute_optimize(lvl) __attribute__ ((optimize(x)))
+#else
+# define attribute_optimize(lvl)
+#endif
+
 #define attribute_unused __attribute__ ((unused))
 
 #if defined __GNUC__ || defined __ICC