[newlib-cygwin] Add a shm_open2 syscall to support upcoming memfd_create

[Sebastian Huber <sh@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=99b66f53154560be576365fba7880f1e2e73de28

commit 99b66f53154560be576365fba7880f1e2e73de28
Author: Kyle Evans <kevans@FreeBSD.org>
Date:   Wed Sep 25 17:59:15 2019 +0000

    Add a shm_open2 syscall to support upcoming memfd_create
    
    shm_open2 allows a little more flexibility than the original shm_open.
    shm_open2 doesn't enforce CLOEXEC on its callers, and it has a separate
    shmflag argument that can be expanded later. Currently the only shmflag is
    to allow file sealing on the returned fd.
    
    shm_open and memfd_create will both be implemented in libc to use this new
    syscall.
    
    __FreeBSD_version is bumped to indicate the presence.
    
    Reviewed by:    kib, markj
    Differential Revision:  https://reviews.freebsd.org/D21393

Diff:
---
 newlib/libc/sys/rtems/include/sys/mman.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/newlib/libc/sys/rtems/include/sys/mman.h b/newlib/libc/sys/rtems/include/sys/mman.h
index f75490c96..6e178d83d 100644
--- a/newlib/libc/sys/rtems/include/sys/mman.h
+++ b/newlib/libc/sys/rtems/include/sys/mman.h
@@ -176,6 +176,12 @@
  * Anonymous object constant for shm_open().
  */
 #define	SHM_ANON		((char *)1)
+
+/*
+ * shmflags for shm_open2()
+ */
+#define	SHM_ALLOW_SEALING		0x00000001
+
 #endif /* __BSD_VISIBLE */
 
 /*