Auto merge of #120238 - joboet:always_confirm_lock_success, r=Mark-Si…

…mulacrum

Always check the result of `pthread_mutex_lock`

Fixes #120147.

Instead of manually adding a list of "good" platforms, I've simply made the check unconditional. pthread's mutex is already quite slow on most platforms, so one single well-predictable branch shouldn't hurt performance too much.