[RFC][WIP] posix: Set mutex type to PTHREAD_MUTEX_ERRORCHECK

[fps]

When looking for a way to debug the deadlock in https://github.com/jackaudio/jack2/issues/395 I stumbled across this advisory:

https://wiki.sei.cmu.edu/confluence/display/c/POS04-C.+Avoid+using+PTHREAD_MUTEX_NORMAL+type+mutex+locks

In the end it didn't detect the deadlock (which is not a proof of it not existing) but I'll leave the PR here for your consideration. Might be helpful in the future..

[falkTX]

having it always on is not the most useful, do we really need it all the time? If you wrap it around a #ifdef BUILD_DEBUG (so that debug builds have it, otherwise everything still the same) I will merge the PR. thanks!