Revert "Add a couple of pthread helper macros"

This reverts commit 8d0ec2403f3444e3a53d16b21f2f8557abd71b55.
Re-introduce our pthread macros (after fixing an earlier typo)

these are so we can differentiate between 'libpthread' and 'libpthread-win32' (whose implementation is subtlely - though annoyingly! - different)
Implement the new pthread macros (for the Waves audio backend)
Add 'libs/pbd/pbd/pthread_utils.h' to our pbd project (msvc)