Fix testcases using __attribute__((noclone)) with Clang

Clang fails to compile a number of files with the following warning:
unknown attribute 'noclone' ignored [-Wunknown-attributes].  This
commit adds a new header, lib/noclone.h, which defines the macro
ATTRIBUTE_NOCLONE accordingly, and updates the relevant testcases
to use it.

gdb/testsuite/ChangeLog:

	* lib/attributes.h: New header.
	* gdb.base/backtrace.c: Include the above. Replace
	__attribute__(noclone)) with ATTRIBUTE_NOCLONE.
	* gdb.base/infcall-nested-structs.c: Likewise.
	* gdb.base/vla-optimized-out.c: Likewise.

1 files changed, 40 insertions, 0 deletions

diff --git a/gdb/testsuite/lib/attributes.h b/gdb/testsuite/lib/attributes.h
new file mode 100644
index 0000000..b66567c
--- /dev/null
+++ b/gdb/testsuite/lib/attributes.h
@@ -0,0 +1,40 @@
+/* This file is part of GDB, the GNU debugger.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   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/>.  */
+
+/* Compatibility macro for __attribute__((noclone)).  */
+
+#ifndef ATTRIBUTES_H
+#define ATTRIBUTES_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __has_attribute
+# if !__has_attribute (noclone)
+#  define ATTRIBUTE_NOCLONE
+# endif
+#endif
+#ifndef ATTRIBUTE_NOCLONE
+# define ATTRIBUTE_NOCLONE __attribute__((noclone))
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ATTRIBUTES_H */