array: mark the array to grow as volatile

This works around strict aliasing rules letting some versions of
GCC (particularly on RHEL 6) thinking that they can skip updating the
size of the array when calculating the next element's offset.

src/array.h

@@ -44,7 +44,7 @@ typedef git_array_t(char) git_array_generic_t;
 /* use a generic array for growth so this can return the new item */
 GIT_INLINE(void *) git_array_grow(void *_a, size_t item_size)
 {
-	git_array_generic_t *a = _a;
+	volatile git_array_generic_t *a = _a;
 	uint32_t new_size = (a->size < 8) ? 8 : a->asize * 3 / 2;
 	char *new_array = git__realloc(a->ptr, new_size * item_size);
 	if (!new_array) {