Include "xalloc.h" first, to check interface.

Include <stdlib.h> unconditionally.

Include exit.h.
(EXIT_FAILURE): Remove; now done by exit.h

lib/xmalloc.c

@@ -21,28 +21,17 @@
 # include <config.h>
 #endif
 
-#include <sys/types.h>
+#include "xalloc.h"
 
-#if STDC_HEADERS
-# include <stdlib.h>
-#else
-void *calloc ();
-void *malloc ();
-void *realloc ();
-void free ();
-#endif
+#include <stdlib.h>
 
 #include "gettext.h"
 #define _(msgid) gettext (msgid)
 #define N_(msgid) msgid
 
 #include "error.h"
+#include "exit.h"
 #include "exitfail.h"
-#include "xalloc.h"
-
-#ifndef EXIT_FAILURE
-# define EXIT_FAILURE 1
-#endif
 
 /* The following tests require AC_PREREQ(2.54).  */