Add annotation to all assembly files to turn off stack-execute bit

See discussion in http://tracker.ceph.com/issues/10114

Building with these changes allows output from readelf like this:

 $ readelf -lW src/.libs/librados.so.2 | grep GNU_STACK
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000
0x000000 RW  0x8

(note the absence of 'X' in 'RW')

Fixes: #10114
Signed-off-by: Dan Mick <dan.mick@redhat.com>
Merge pull request #2946 from ceph/wip-execstack

Add annotation to all assembly files to turn off stack-execute bit

Reviewed-by: Sage Weil <sage@redhat.com>