Include <stdlib.h>, for malloc; don't bother with stddef.h.

rpl_malloc returns void *, not char *.

lib/malloc.c

@@ -22,14 +22,12 @@
 #endif
 #undef malloc
 
-#include <stddef.h>
-
-char *malloc ();
+#include <stdlib.h>
 
 /* Allocate an N-byte block of memory from the heap.
    If N is zero, allocate a 1-byte block.  */
 
-char *
+void *
 rpl_malloc (size_t n)
 {
   if (n == 0)