[newlib-cygwin] Declare the pthread_rwlock_* functions if __cplusplus >= 201402L

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=59847b5d737191b8b42085d6447a8060074b8195

commit 59847b5d737191b8b42085d6447a8060074b8195
Author: Ken Brown <kbrown@cornell.edu>
Date:   Wed May 30 16:19:01 2018 -0400

    Declare the pthread_rwlock_* functions if __cplusplus >= 201402L
    
    Some of these functions are used in the <shared_mutex> C++ header.

Diff:
---
 winsup/cygwin/include/pthread.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/include/pthread.h b/winsup/cygwin/include/pthread.h
index 3dfc2bc..fed6165 100644
--- a/winsup/cygwin/include/pthread.h
+++ b/winsup/cygwin/include/pthread.h
@@ -187,7 +187,7 @@ int pthread_spin_unlock (pthread_spinlock_t *);
 #endif
 
 /* RW Locks */
-#if __XSI_VISIBLE >= 500 || __POSIX_VISIBLE >= 200112
+#if __XSI_VISIBLE >= 500 || __POSIX_VISIBLE >= 200112 || __cplusplus >= 201402L
 int pthread_rwlock_destroy (pthread_rwlock_t *rwlock);
 int pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr);
 int pthread_rwlock_rdlock (pthread_rwlock_t *rwlock);