assert: Add static_assert macro

See the C11 standard 7.2 §3

The definition is copied from glibc.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>

include/assert.h

@@ -76,3 +76,8 @@ __END_DECLS
 # endif
 
 #endif /* NDEBUG.  */
+
+#if defined __USE_ISOC11 && !defined __cplusplus
+# undef static_assert
+# define static_assert _Static_assert
+#endif