util: add missing xregion_alloc

Fixes commit 837b0948 ("box: handle region_alloc failure in
tuple_field_map_create_plain").

NO_DOC=build fix
NO_TEST=build fix
NO_CHANGELOG=build fix

src/trivia/util.h

@@ -126,6 +126,7 @@ strnindex(const char *const *haystack, const char *needle, uint32_t len,
 #define xrealloc(ptr, size)	xalloc_impl((size), realloc, (ptr), (size))
 #define xstrdup(s)		xalloc_impl(strlen((s)) + 1, strdup, (s))
 #define xstrndup(s, n)		xalloc_impl((n) + 1, strndup, (s), (n))
+#define xregion_alloc(p, size)	xalloc_impl((size), region_alloc, (p), (size))
 
 /** \cond public */