environ-selftests: Ignore -Wself-move warning

clang gives this warning:

 ..../gdb/unittests/environ-selftests.c:139:7: error: explicitly moving variable of type 'gdb_environ' to itself [-Werror,-Wself-move]
   env = std::move (env);
   ~~~ ^            ~~~

Ignoring the warning locally is the right thing to do, since it warns
about behavior we want to unit test, while an explicit self-move in
real code would likely be a mistake that we'd want to catch.

To avoid cluttering the code with preprocessor conditionals, this
commit adds the file common/diagnostics.h, in which we can put macros
used to control compiler diagnostics.

GCC enhancement request here:
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81159

gdb/ChangeLog:
2017-06-22  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@ericsson.com>

	* unittests/environ-selftests.c (run_tests): Ignore -Wself-move
	warning.
	* common/diagnostics.h: New file.

1 files changed, 40 insertions, 0 deletions

diff --git a/gdb/common/diagnostics.h b/gdb/common/diagnostics.h
new file mode 100644
index 0000000..5a63bfd
--- /dev/null
+++ b/gdb/common/diagnostics.h
@@ -0,0 +1,40 @@
+/* Copyright (C) 2017 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 COMMON_DIAGNOSTICS_H
+#define COMMON_DIAGNOSTICS_H
+
+#include "common/preprocessor.h"
+
+#ifdef __GNUC__
+# define DIAGNOSTIC_PUSH _Pragma ("GCC diagnostic push")
+# define DIAGNOSTIC_POP _Pragma ("GCC diagnostic pop")
+# define DIAGNOSTIC_IGNORE(option) \
+  _Pragma (STRINGIFY (GCC diagnostic ignored option))
+#else
+# define DIAGNOSTIC_PUSH
+# define DIAGNOSTIC_POP
+# define DIAGNOSTIC_IGNORE(option)
+#endif
+
+#ifdef __clang__
+# define DIAGNOSTIC_IGNORE_SELF_MOVE DIAGNOSTIC_IGNORE ("-Wself-move")
+#else
+# define DIAGNOSTIC_IGNORE_SELF_MOVE
+#endif
+
+#endif /* COMMON_DIAGNOSTICS_H */