Update gnulib to a3a946f670718d0dee5a7425ad5ac0a29fb46ea1

This fixes https://lists.gnu.org/archive/html/guile-devel/2021-04/msg00009.html

lib/realloc.c

@@ -0,0 +1,85 @@
+/* realloc() function that is glibc compatible.
+
+   Copyright (C) 1997, 2003-2004, 2006-2007, 2009-2021 Free Software
+   Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering and Bruno Haible */
+
+#define _GL_USE_STDLIB_ALLOC 1
+#include <config.h>
+
+/* Only the AC_FUNC_REALLOC macro defines 'realloc' already in config.h.  */
+#ifdef realloc
+# define NEED_REALLOC_GNU 1
+/* Whereas the gnulib module 'realloc-gnu' defines HAVE_REALLOC_GNU.  */
+#elif GNULIB_REALLOC_GNU && !HAVE_REALLOC_GNU
+# define NEED_REALLOC_GNU 1
+#endif
+
+/* Infer the properties of the system's malloc function.
+   The gnulib module 'malloc-gnu' defines HAVE_MALLOC_GNU.  */
+#if GNULIB_MALLOC_GNU && HAVE_MALLOC_GNU
+# define SYSTEM_MALLOC_GLIBC_COMPATIBLE 1
+#endif
+
+#include <stdlib.h>
+
+/* A function definition is only needed if NEED_REALLOC_GNU is defined above
+   or if the module 'realloc-posix' requests it.  */
+#if NEED_REALLOC_GNU || (GNULIB_REALLOC_POSIX && !HAVE_REALLOC_POSIX)
+
+# include <errno.h>
+
+/* Change the size of an allocated block of memory P to N bytes,
+   with error checking.  If N is zero, change it to 1.  If P is NULL,
+   use malloc.  */
+
+void *
+rpl_realloc (void *p, size_t n)
+{
+  void *result;
+
+# if NEED_REALLOC_GNU
+  if (n == 0)
+    {
+      n = 1;
+
+      /* In theory realloc might fail, so don't rely on it to free.  */
+      free (p);
+      p = NULL;
+    }
+# endif
+
+  if (p == NULL)
+    {
+# if GNULIB_REALLOC_GNU && !NEED_REALLOC_GNU && !SYSTEM_MALLOC_GLIBC_COMPATIBLE
+      if (n == 0)
+        n = 1;
+# endif
+      result = malloc (n);
+    }
+  else
+    result = realloc (p, n);
+
+# if !HAVE_REALLOC_POSIX
+  if (result == NULL)
+    errno = ENOMEM;
+# endif
+
+  return result;
+}
+
+#endif