* thread.h (pthread::init_mainthread): Remove function parameter.

* thread.h (pthread::init_mainthread): Remove function parameter.
(MTinterface::Init): Ditto.
* thread.cc (MTinterface::Init): Remove function parameter.
Always initialize reent_key.
(pthread::init_mainthread): Remove function parameter.
(MTinterface::fixup_after_fork): Fix pthread::init_mainthread call.
* dcrt0.cc (dll_crt_0_1) Fix calls to MTinterface::Init and
pthread::init_mainthread.
Call pthread::init_mainthread only when not forked.