WIP: Add non-recursive thread lock support for Windows ##util

[randomjack94dev]

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• I've added tests (optional)
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Description

Use SRWLocks to handle non-recursive thread locks on Windows (as suggested by the TODO comment). We use a union of CRITICAL_SECTION and SRWLOCK tagged by 'recursive' boolean flag to cover both types of locks.

[randomjack94dev]

@trufae

It doesn't seem to me like it's going to break something, but I am not entirely sure and you certainly have more experience in this regard than me. Any thoughts?

I don't think I fully understand the purpose of r_w32 wrappers (targeting older versions of Windows?), so I have a question about those. As you can see, I added r_w32_SleepConditionVariableSRW in analogy with r_w32_SleepConditionVariableCS, but haven't done so for other SRWLock functions (as CS-functions which were already used for implementing locks are called without wrappers). But since SRW-locks require Vista/2008 CI w64-mingw build yields warnings about their implicit declaration. Should I also add r_w32 wrappers for SRWLock functions used in util/thread_lock.c?

Any feedback is appreciated, thank you!