reallocarray: simplify

* lib/reallocarray.c (reallocarray): Use simpler workaround
for realloc glitch, which does not involve malloc.
* modules/reallocarray (Depends-on): Remove malloc-posix.

ChangeLog

@@ -1,3 +1,10 @@
+2024-10-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+	reallocarray: simplify
+	* lib/reallocarray.c (reallocarray): Use simpler workaround
+	for realloc glitch, which does not involve malloc.
+	* modules/reallocarray (Depends-on): Remove malloc-posix.
+
 2024-10-23  Paul Eggert  <eggert@cs.ucla.edu>
 
 	ialloc: fix realloc-gnu dependency

lib/reallocarray.c

@@ -33,17 +33,11 @@ reallocarray (void *ptr, size_t nmemb, size_t size)
       return NULL;
     }
 
-  /* Avoid calling realloc (ptr, 0), since that is undefined behaviour in
+  /* Work around realloc glitch by treating a 0 size as if it were 1,
-     ISO C 23 and since the GNU libc behaviour may possibly change.  */
+     to avoid undefined behavior in strict C23 platforms,
+     and so that returning NULL is equivalent to failing.  */
   if (nbytes == 0)
-    {
+    nbytes = 1;
-      void *new_ptr = malloc (1);
-      if (new_ptr == NULL)
-        /* errno is set here.  */
-        return NULL;
-      free (ptr);
-      return new_ptr;
-    }
 
   /* Call realloc, setting errno to ENOMEM on failure.  */
   return realloc (ptr, nbytes);

modules/reallocarray

@@ -8,7 +8,6 @@ m4/reallocarray.m4
 
 Depends-on:
 extensions
-malloc-posix   [test $HAVE_REALLOCARRAY = 0 || test $REPLACE_REALLOCARRAY = 1]
 realloc-posix  [test $HAVE_REALLOCARRAY = 0 || test $REPLACE_REALLOCARRAY = 1]
 stdckdint      [test $HAVE_REALLOCARRAY = 0 || test $REPLACE_REALLOCARRAY = 1]
 stdlib