Disable implicit multi-threaded mode for Win32 to avoid LOCK crash

Disable implicit multi-threaded mode for Win32 to avoid LOCK crash
(fix commit d5c6531)

* include/private/gc_locks.h [GC_ALWAYS_MULTITHREADED] (GC_need_to_lock):
Do not define to TRUE unless USE_PTHREAD_LOCKS or USE_SPIN_LOCK; issue
#error otherwise (excluding CPPCHECK case) as PCR and Windows-based
lock implementation requires it to be initialized first.
* include/private/gc_locks.h [UNCOND_LOCK && !LOCK && LINT2] (LOCK,
UNLOCK): Define (to UNCOND_[UN]LOCK) only if USE_PTHREAD_LOCKS.