reallocarray: New module

reallocarray is a new function in glibc 2.26 to safely allocate an array
of memory locations with integer overflow protection.
* MODULES.html.sh: Add reallocarray.
* doc/glibc-functions/reallocarray.texi: Documentation for reallocarray.
* lib/reallocarray.c: New file to implement module reallocarray.
* lib/stdlib.in.h: Add function declarations for reallocarray.
* m4/reallocarray.m4: New file.
* m4/stdlib_h.m4: Declare reallocarray.
* modules/reallocarray: New file.
* modules/reallocarray-test: New file.
* modules/stdlib: Coerce stdlib.h to export reallocarray.
* tests/test-reallocarray.c: New test.

modules/reallocarray

@@ -0,0 +1,32 @@
+Description:
+reallocarray() function that is glibc compatible.
+
+Files:
+lib/reallocarray.c
+m4/reallocarray.m4
+
+Depends-on:
+extensions
+xalloc-oversized
+realloc-gnu
+stdlib
+
+configure.ac:
+gl_FUNC_REALLOCARRAY
+if test $HAVE_REALLOCARRAY = 0; then
+  AC_LIBOBJ([reallocarray])
+  gl_PREREQ_REALLOCARRAY
+fi
+gl_MODULE_INDICATOR([reallocarray])
+gl_STDLIB_MODULE_INDICATOR([reallocarray])
+
+Makefile.am:
+
+Include:
+<stdlib.h>
+
+License:
+GPLv3+
+
+Maintainer:
+all