io_pgetevents() will not change the signal mask.  Mark it const to make
it clear and to reduce the need for casts in user code.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAvi Kivity <avi@scylladb.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
[hch: reapply the patch that got incorrectly reverted]
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>