[2.27 COMMITTED] Use _STRUCT_TIMESPEC as guard in <bits/types/struct_timespec.h> [BZ #23349]

[fweimer@redhat.com (Florian Weimer)]

After commit d76d3703551a362b472c866b5b6089f66f8daa8e ("Fix missing
timespec definition for sys/stat.h (BZ #21371)") in combination with
kernel UAPI changes, GCC sanitizer builds start to fail due to a
conflicting definition of struct timespec in <linux/time.h>.  Use
_STRUCT_TIMESPEC as the header file inclusion guard, which is already
checked in the kernel header, to support including <linux/time.h> and
<sys/stat.h> in the same translation unit.

(cherry picked from commit c1c2848b572ea7f92b7fa81dd5b1b9ef7c69b83b)

2018-06-28  Florian Weimer  <fweimer@redhat.com>

	[BZ #23349]
	* time/bits/types/struct_timespec.h: Change header inclusion guard to
	_STRUCT_TIMESPEC.

diff --git a/NEWS b/NEWS
index 2dab66e851..f6e33734c8 100644
--- a/NEWS
+++ b/NEWS
@@ -80,6 +80,7 @@ The following bugs are resolved with this release:
   [23236] Harden function pointers in _IO_str_fields
   [23259] Unsubstituted ${ORIGIN} remains in DT_NEEDED for AT_SECURE
   [23264] libc: posix_spawnp wrongly executes ENOEXEC in non compat mode
+  [23349] Various glibc headers no longer compatible with <linux/time.h>
 
 \f
 Version 2.27
diff --git a/time/bits/types/struct_timespec.h b/time/bits/types/struct_timespec.h
index 644db9fdb6..5b77c52b4f 100644
--- a/time/bits/types/struct_timespec.h
+++ b/time/bits/types/struct_timespec.h
@@ -1,5 +1,6 @@
-#ifndef __timespec_defined
-#define __timespec_defined 1
+/* NB: Include guard matches what <linux/time.h> uses.  */
+#ifndef _STRUCT_TIMESPEC
+#define _STRUCT_TIMESPEC 1
 
 #include <bits/types.h>