Avoid data race in finalized_count (gctest)

Avoid data race in finalized_count (gctest)

* tests/test.c (FINALIZER_LOCK, FINALIZER_UNLOCK): New macro.
* tests/test.c [GC_PTHREADS] (incr_lock): Move static variable out
of finalizer() and mktree() (use a single lock variable to access
finalized_count in finalizer, mktree and tree_test).
* tests/test.c (dropped_something): Change type back to int; remove
volatile.
* tests/test.c (finalizer, mktree): Use FINALIZER_[UN]LOCK() instead
of PCR_ThCrSec_Enter/ExitSys(), pthread_mutex_[un]lock(),
Enter/LeaveCriticalSection().
* tests/test.c (tree_test): Use FINALIZER_[UN]LOCK() to avoid data
race when accessing finalized_count and dropped_something; do not use
AO_load() and AO_store() to access dropped_something.
* tests/test.c