Fix TLS Segfault on various mac versions
Accepted by: @wraitii
Tested by: Tobbi, Servo, HMS-Surprise
Thread: https://wildfiregames.com/forum/index.php?/topic/25120-macos-osx-rc-bundles/page/2/&tab=comments#comment-368603
Fixes #5386
Differential Revision: https://code.wildfiregames.com/D1772