support: Add xpthread_kill

Checked on x86_64-linux-gnu.

support/Makefile

@@ -141,6 +141,7 @@ libsupport-routines = \
   xpthread_join \
   xpthread_key_create \
   xpthread_key_delete \
+  xpthread_kill \
   xpthread_mutex_consistent \
   xpthread_mutex_destroy \
   xpthread_mutex_init \

support/xpthread_kill.c

@@ -0,0 +1,26 @@
+/* pthread_kill with error checking.
+   Copyright (C) 2021 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 <signal.h>
+#include <support/xthread.h>
+
+void
+xpthread_kill (pthread_t thr, int signo)
+{
+  xpthread_check_return ("pthread_kill", pthread_kill (thr, signo));
+}

support/xthread.h

@@ -75,6 +75,8 @@ void xpthread_attr_setstacksize (pthread_attr_t *attr,
 void xpthread_attr_setguardsize (pthread_attr_t *attr,
 				 size_t guardsize);
 
+void xpthread_kill (pthread_t thr, int signo);
+
 /* Return the stack size used on support_set_small_thread_stack_size.  */
 size_t support_small_thread_stack_size (void);
 /* Set the stack size in ATTR to a small value, but still large enough