ARC: Thread Local Storage support

This includes all 4 TLS addressing models

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/arc/libc-tls.c

@@ -0,0 +1,27 @@
+/* Thread-local storage handling in the ELF dynamic linker.  ARC version.
+   Copyright (C) 2020 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 <csu/libc-tls.c>
+#include <dl-tls.h>
+
+void *
+__tls_get_addr (tls_index *ti)
+{
+  dtv_t *dtv = THREAD_DTV ();
+  return (char *) dtv[1].pointer.val + ti->ti_offset;
+}