support: Add xsetlocale function

(cherry picked from commit cce35a50c1)

support/Makefile

@@ -146,6 +146,7 @@ libsupport-routines = \
   xrealloc \
   xrecvfrom \
   xsendto \
+  xsetlocale \
   xsetsockopt \
   xsigaction \
   xsignal \

support/support.h

@@ -91,6 +91,7 @@ char *xasprintf (const char *format, ...)
   __attribute__ ((format (printf, 1, 2), malloc));
 char *xstrdup (const char *);
 char *xstrndup (const char *, size_t);
+char *xsetlocale (int category, const char *locale);
 
 /* These point to the TOP of the source/build tree, not your (or
    support's) subdirectory.  */

support/xsetlocale.c

@@ -0,0 +1,30 @@
+/* setlocale with error checking.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library 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 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <support/check.h>
+
+#include <locale.h>
+
+char *
+xsetlocale (int category, const char *locale)
+{
+  char *p = setlocale (category, locale);
+  if (p == NULL)
+    FAIL_EXIT1 ("error: setlocale (%d, \"%s\")\n", category, locale);
+  return p;
+}