ARC: Linux Startup and Dynamic Loading

A big shoutout to Cupertino Miranda <cmiranda@synopsys.com> for his
valuable contribution in initial bringup and debugging on Linux and
later in solving pesky unwinding/cancelation failures in testsuite.

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

sysdeps/unix/sysv/linux/arc/ldsodefs.h

@@ -0,0 +1,32 @@
+/* Run-time dynamic linker data structures for loaded ELF shared objects. ARC
+   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/>.  */
+
+#ifndef	_LDSODEFS_H
+
+/* Get the real definitions.  */
+#include_next <ldsodefs.h>
+
+/* Now define our stuff.  */
+
+/* We need special support to initialize DSO loaded for statically linked
+   binaries.  */
+extern void _dl_static_init (struct link_map *map);
+#undef DL_STATIC_INIT
+#define DL_STATIC_INIT(map) _dl_static_init (map)
+
+#endif /* ldsodefs.h */