[newlib-cygwin] declaration of ppoll() by poll.h should be guarded by _GNU_SOURCE

[Jon TURNEY]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=b568f92c505aaa923160eca93935995dd6b88b16

commit b568f92c505aaa923160eca93935995dd6b88b16
Author: Jon Turney <jon.turney@dronecode.org.uk>
Date:   Mon Mar 27 15:19:36 2017 +0100

    declaration of ppoll() by poll.h should be guarded by _GNU_SOURCE
    
    Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>

Diff:
---
 winsup/cygwin/include/sys/poll.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/winsup/cygwin/include/sys/poll.h b/winsup/cygwin/include/sys/poll.h
index 8228278..0da4c3f 100644
--- a/winsup/cygwin/include/sys/poll.h
+++ b/winsup/cygwin/include/sys/poll.h
@@ -39,9 +39,11 @@ struct pollfd {
 typedef unsigned int nfds_t;
 
 extern int poll __P ((struct pollfd *fds, nfds_t nfds, int timeout));
+#if __GNU_VISIBLE
 extern int ppoll __P ((struct pollfd *fds, nfds_t nfds,
 		       const struct timespec *timeout_ts,
 		       const sigset_t *sigmask));
+#endif
 
 __END_DECLS