Partial backport of this upstream commit:

commit e15f7de60c26bb75fe1923b17c5f0461164d1a41

Author: Zack Weinberg <zackw@panix.com>

Date:   Sun Nov 20 20:46:30 2016 -0500

    Split DIAG_* macros to new header libc-diag.h.

Only the include/libc-diag.h header file is added.

diff --git a/include/libc-diag.h b/include/libc-diag.h

new file mode 100644

index 0000000000000000..db138c63b1573256

--- /dev/null

+++ b/include/libc-diag.h

@@ -0,0 +1,74 @@

+/* Macros for controlling diagnostic output from the compiler.

+   Copyright (C) 2014-2017 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

+   <http://www.gnu.org/licenses/>.  */

+

+#ifndef _LIBC_DIAG_H

+#define _LIBC_DIAG_H 1

+

+/* Ignore the value of an expression when a cast to void does not

+   suffice (in particular, for a call to a function declared with

+   attribute warn_unused_result).  */

+#define ignore_value(x) \

+  ({ __typeof__ (x) __ignored_value = (x); (void) __ignored_value; })

+

+/* The macros to control diagnostics are structured like this, rather

+   than a single macro that both pushes and pops diagnostic state and

+   takes the affected code as an argument, because the GCC pragmas

+   work by disabling the diagnostic for a range of source locations

+   and do not work when all the pragmas and the affected code are in a

+   single macro expansion.  */

+

+/* Push diagnostic state.  */

+#define DIAG_PUSH_NEEDS_COMMENT _Pragma ("GCC diagnostic push")

+

+/* Pop diagnostic state.  */

+#define DIAG_POP_NEEDS_COMMENT _Pragma ("GCC diagnostic pop")

+

+#define _DIAG_STR1(s) #s

+#define _DIAG_STR(s) _DIAG_STR1(s)

+

+/* Ignore the diagnostic OPTION.  VERSION is the most recent GCC

+   version for which the diagnostic has been confirmed to appear in

+   the absence of the pragma (in the form MAJOR.MINOR for GCC 4.x,

+   just MAJOR for GCC 5 and later).  Uses of this pragma should be

+   reviewed when the GCC version given is no longer supported for

+   building glibc; the version number should always be on the same

+   source line as the macro name, so such uses can be found with grep.

+   Uses should come with a comment giving more details of the

+   diagnostic, and an architecture on which it is seen if possibly

+   optimization-related and not in architecture-specific code.  This

+   macro should only be used if the diagnostic seems hard to fix (for

+   example, optimization-related false positives).  */

+#define DIAG_IGNORE_NEEDS_COMMENT(version, option)     \

+  _Pragma (_DIAG_STR (GCC diagnostic ignored option))

+

+/* Similar to DIAG_IGNORE_NEEDS_COMMENT the following macro ignores the

+   diagnostic OPTION but only if optimizations for size are enabled.

+   This is required because different warnings may be generated for

+   different optimization levels.  For example a key piece of code may

+   only generate a warning when compiled at -Os, but at -O2 you could

+   still want the warning to be enabled to catch errors.  In this case

+   you would use DIAG_IGNORE_Os_NEEDS_COMMENT to disable the warning

+   only for -Os.  */

+#ifdef __OPTIMIZE_SIZE__

+# define DIAG_IGNORE_Os_NEEDS_COMMENT(version, option) \

+  _Pragma (_DIAG_STR (GCC diagnostic ignored option))

+#else

+# define DIAG_IGNORE_Os_NEEDS_COMMENT(version, option)

+#endif

+

+#endif /* libc-diag.h */