Define SET/UNSET_MARK_LOCK_HOLDER macros to set/check GC_acquire_mark_lock

Define SET/UNSET_MARK_LOCK_HOLDER macros to set/check GC_acquire_mark_lock
(refactoring)

* pthread_support.c (SET_MARK_LOCK_HOLDER, UNSET_MARK_LOCK_HOLDER):
New macro (defined to no action unless GC_ASSERTIONS).
* win32_threads.c (SET_MARK_LOCK_HOLDER, UNSET_MARK_LOCK_HOLDER):
Likewise.
* pthread_support.c (GC_acquire_mark_lock, GC_release_mark_lock,
GC_wait_builder, GC_wait_marker): Use [UN]SET_MARK_LOCK_HOLDER
(instead of GC_mark_lock_holder setters and checkers).
* win32_threads.c (GC_acquire_mark_lock, GC_release_mark_lock,
GC_wait_builder, GC_wait_marker): Likewise.
* win32_threads.c (GC_mark_lock_holder): Change type to DWORD unless
GC_PTHREADS_PARAMARK defined.
* win32_threads.c (GC_acquire_mark_lock, GC_notify_all_builder):
Remove unnecessary cast of GetCurrentThreadId() result.