Use ISO C99 __func__ instead of GNU __FUNCTION__

xs.h

@@ -52,7 +52,7 @@ typedef char xs_data;
 
 void *xs_free(void *ptr);
 void *_xs_realloc(void *ptr, size_t size, const char *file, int line, const char *func);
-#define xs_realloc(ptr, size) _xs_realloc(ptr, size, __FILE__, __LINE__, __FUNCTION__)
+#define xs_realloc(ptr, size) _xs_realloc(ptr, size, __FILE__, __LINE__, __func__)
 int _xs_blk_size(int sz);
 void _xs_destroy(char **var);
 #define xs_debug() raise(SIGTRAP)