Pre-flight SkTLS_pthread changes for C++17

Looks like this is what the CFI bots tripped on,
so maybe there's something more real going on here.

I think we can try again in Chromium after this?

Change-Id: I6f59aeae01df130a21c64b5218b4d21238e343d7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253636
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed