compiler/pthread: port latest version

compiler/pthread: port latest version

Fixed:
- TLS keys: threads overwriting each other's keys, destructors not being
called per thread
- mutexes: better compatibility with the normal and errorchecking ones
- thread creation: no longer wastes the signals of the parent task
- once functions: fixed slow initializers, multiple threads could enter
- cleanup handlers: the functions were never called
- a lot of non-standard compliant behavior fixed

New features:
- timed mutexes
- rwlocks
- barriers
- semaphores
- thread cancellation: fairly limited, deferred only. adding all the
cancellation points would require C library integration.

git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@50228 fb15a70f-31f2-0310-bbcc-cdcc74a49acc