There is no reason to define malloc() to xmalloc() in this context.

main/alloca.c

@@ -77,21 +77,6 @@ typedef char *pointer;
 #define	NULL	0
 #endif
 
-/* Different portions of Emacs need to call different versions of
-   malloc.  The Emacs executable needs alloca to call xmalloc, because
-   ordinary malloc isn't protected from input signals.  On the other
-   hand, the utilities in lib-src need alloca to call malloc; some of
-   them are very simple, and don't have an xmalloc routine.
-
-   Non-Emacs programs expect this to call use xmalloc.
-
-   Callers below should use malloc.  */
-
-#ifndef emacs
-#define malloc xmalloc
-#endif
-extern pointer malloc ();
-
 /* Define STACK_DIRECTION if you know the direction of stack
    growth for your system; otherwise it will be automatically
    deduced at run-time.
@@ -169,7 +154,7 @@ static header *last_alloca_header = NULL;	/* -> last alloca header.  */
 
 pointer
 alloca (size)
-     unsigned size;
+     size_t size;
 {
   auto char probe;		/* Probes stack depth: */
   register char *depth = ADDRESS_FUNCTION (probe);