[Android] Only warn about existing SIGSYS handlers pre-O.

Bug: 166704
Change-Id: I3f95a10ea12e1155272a0d3213e1cc0eb4c7a607
Reviewed-on: https://chromium-review.googlesource.com/521388
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Alexandre Elias <aelias@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#476432}
1 file changed