[Issue 21919] darwin: SEGV in core.thread tests on OSX 11

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #2 from Iain Buclaw <ibuclaw at gdcproject.org> ---
$ sw_vers
ProductName:    macOS
ProductVersion: 11.1
BuildVersion:   20C69

$ clang --version
Apple clang version 12.0.0 (clang-1200.0.32.27)

$ xcodebuild -version
Xcode 12.2
Build version 12B45b

$ uname -v
Darwin Kernel Version 20.2.0: Wed Dec  2 20:39:59 PST 2020;
root:xnu-7195.60.75~1/RELEASE_X86_64

druntime: a79bb0eb0424f77159eb72e1c527db3b2ae2a57d

dmd: 97aa2ae5ee19ce6a2979ca1627479df713f99252

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