* src/mm/cacao-gc/gc.c (gc_global_lock): Removed obsolete global lock.

* src/mm/cacao-gc/gc.c (gc_global_lock): Removed obsolete global lock.
(gc_collect): Use GC mutex as global gc lock.
(gc_reference_register_intern, gc_reference_unregister_intern): Use GC mutex to
lock the reference lists.

* src/mm/cacao-gc/gc.h (GC_MUTEX_LOCK, GC_MUTEX_UNLOCK): Added macros.

* src/threads/native/threads.c [ENABLE_GC_CACAO] (mutex_gc): Added GC mutex.
[ENABLE_GC_CACAO] (threads_mutex_gc_lock, threads_mutex_gc_unlock): Implemented.

* src/threads/threads-common.h [ENABLE_GC_CACAO]
(threads_mutex_gc_lock, threads_mutex_gc_unlock): Added prototypes.