Use xmalloc rather than malloc

Use xmalloc rather than malloc

As far as I can tell, the following comment is false nowadays.
/* Calls to m-alloc get turned by sed into xm-alloc.  */

Remove it, and call xmalloc.

	* ldlex.l (yy_create_string_buffer): Use xmalloc rather than malloc.
	* lexsup.c (parse_args): Likewise.