Needed by Underworld Island (Steam ID: 2150830) to skip videos properly.
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v3: mfmediaengine: Implement media_engine_GetSeekable().
mfmediaengine/tests: Test IMFMediaEngine::GetSeekable().
https://gitlab.winehq.org/wine/wine/-/merge_requests/3536
This comes from behavioral study of Windows, which doesn't seem to check if the
lock is actually exclusively held, and just simply decrement the value stored
in the lock.
This fixes a dead lock which prevents WeCom from starting up.
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v12: ntdll: An implementation of SRWLOCK that closer matches Windows'.
include: add atomic read/write of pointers
https://gitlab.winehq.org/wine/wine/-/merge_requests/3504