Fix semaphore for macOS

[hkr]

Pull Request checklist

Note: these are not necessarily requirements

• [x] I reformatted the code with clang-format
• [x] I checked to make sure my submission worked
• [x] I am the author of submission or have permission from the original author
• [ ] Requires update of the PS2SDK
• [ ] Requires update of the gsKit
• [ ] Others (please specify below)

Pull Request description

Use of named semaphores had issues (use of sem_open is missing mandatory parameters: initial semaphore value permissions), which caused essentially an infinite loop at least on my system.

This change replaces named semaphore with a semaphore built on top of pthread condvar.

[uyjulian]

Thank you. I didn't really look in the direction of the pthread API, but good to know it's possible to wrap that.