Add configure test for alloc_size attribute.

configure.ac

@@ -428,6 +428,17 @@ if test "x${je_cv_tls_model}" = "xyes" ; then
 else
   AC_DEFINE([JEMALLOC_TLS_MODEL], [ ])
 fi
+dnl Check for alloc_size attribute support.
+SAVED_CFLAGS="${CFLAGS}"
+JE_CFLAGS_APPEND([-Werror])
+JE_COMPILABLE([alloc_size attribute], [],
+              [#include <stdlib.h>
+               static void *foo(size_t size) __attribute__((alloc_size(1)));],
+              [je_cv_alloc_size])
+CFLAGS="${SAVED_CFLAGS}"
+if test "x${je_cv_alloc_size}" = "xyes" ; then
+  AC_DEFINE([JEMALLOC_HAVE_ATTR_ALLOC_SIZE], [ ])
+fi
 
 dnl Support optional additions to rpath.
 AC_ARG_WITH([rpath],