[Issue 20256] problem with signal handling and parallel GC on linux

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20256

--- Comment #3 from igor.khasilev at gmail.com ---
To be clear - I'm not against parallel GC, just against unexpected behavior. I
can spend time and prepare PR if it hav any chance to be accepted.

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