Eliminate TSan warnings for all counters and A.aa variable (gctest)

Eliminate TSan warnings for all counters and A.aa variable (gctest)

Now most of the counters in gctest are updated using atomic increment.
And, the values of gctest dropped_something and A.aa variables are
updated and fetch using the atomic primitives.

* tests/test.c [!AO_CLEAR] (AO_t): Define.
* tests/test.c [!AO_HAVE_load] (AO_load): Define (as a non-atomic
operation).
* tests/test.c [!AO_HAVE_store] (AO_store): Likewise.
* tests/test.c [!AO_HAVE_fetch_and_add1] (AO_fetch_and_add1): Likewise.
* tests/test.c (stubborn_count, uncollectable_count,
collectable_count, atomic_count, realloc_count): Change type from int
to AO_t; add volatile qualifier; update comment; remove FIXME.
* tests/test.c (extra_count): Define unconditionally; change type from
int to AO_t; add volatile qualifier; update comment.
* tests/test.c [!VERY_SMALL_CONFIG] (cons): Use AO_fetch_and_add1 to
get and update the values of extra_count and stubborn_count.
* tests/test.c (small_cons_uncollectable): Use AO_fetch_and_add1 to
update the value of uncollectable_count.
* tests/test.c [!DBG_HDRS_ALL] (run_one_test): Likewise.
* tests/test.c [GC_GCJ_SUPPORT] (gcj_cons): Remove obj_cnt static
variable; use extra_count instead of obj_cnt; use AO_fetch_and_add1 to
get and update the value of extra_count.
* tests/test.c (A): Add volatile qualifier; change the type of aa
field from sexpr to AO_t.
* tests/test.c (a): Do not define (and undefine).
* tests/test.c (a_set, a_get): New macro (that uses AO_store/load).
* tests/test.c (reverse_test_inner): Use a_set() and a_get() to store
and fetch the value of a, respectively; use AO_fetch_and_add1 to
update the value of realloc_count.
* tests/test.c (dropped_something): Change type from int to AO_t.
* tests/test.c (counter): Remove.
* tests/test.c (mktree): Use extra_count instead of counter; use
AO_fetch_and_add1 to update the value of extra_count.
* tests/test.c [GC_PTHREADS && !SMALL_CONFIG && !GC_DEBUG]
(alloc8bytes): Use AO_fetch_and_add1 to update the value of
uncollectable_count.
* tests/test.c (alloc_small, run_one_test): Use AO_fetch_and_add1 to
update the value of atomic_count.
* tests/test.c (tree_test): Use AO_load and AO_store to get and set
the value of dropped_something, respectively.
* tests/test.c (check_heap_stats): Cast uncollectable_count,
atomic_count, stubborn_count, realloc_count to int in printf() call.