Protect nat/gdb_thread_db.h against multiple inclusion.

Fixes a build error due to typedef redefinition with some compilers.

Also added missing copyright header.

gdb/
	* nat/gdb_thread_db.h: Add copyright header.
	Protect against multiple inclusion.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2015-08-05  Ulrich Weigand  <uweigand@de.ibm.com>
+
+	* nat/gdb_thread_db.h: Add copyright header.
+	Protect against multiple inclusion.
+
 2015-08-05  Yao Qi  <yao.qi@linaro.org>
 
 	* aarch64-linux-nat.c (get_thread_id): Remove.

gdb/nat/gdb_thread_db.h

@@ -1,3 +1,23 @@
+/* Copyright (C) 2000-2015 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDB_THREAD_DB_H
+#define GDB_THREAD_DB_H 1
+
 #ifdef HAVE_THREAD_DB_H
 #include <thread_db.h>
 #else
@@ -52,3 +72,5 @@ typedef td_err_e (td_thr_tlsbase_ftype) (const td_thrhandle_t *th,
 
 typedef const char ** (td_symbol_list_ftype) (void);
 typedef td_err_e (td_ta_delete_ftype) (td_thragent_t *);
+
+#endif /* GDB_THREAD_DB_H */