[gc counters] avoid using Interlocked*64 functions as they are broken on some arches...

[gc counters] avoid using Interlocked*64 functions as they are broken on some arches (#5451)

They are implemented via a global lock, which can lead to deadlooks in
some situations, e.g.

```
-0  0xb6c92e14 in sigsuspend () from /lib/arm-linux-gnueabi/libc.so.6
-1  0x0043f3b4 in suspend_signal_handler (_dummy=35, info=0xb4afe6d0, context=0xb4afe750) at mono-threads-posix-signals.c:177
-2  <signal handler called>
-3  0xb6de6bc4 in __pthread_mutex_unlock_usercnt () from /lib/arm-linux-gnueabi/libpthread.so.0
-4  0x00440f00 in InterlockedCompareExchange64 (dest=0x530700 <worker+64>, exch=0, comp=0) at atomic.c:578
-5  0x002f228c in InterlockedRead64 (src=0x530700 <worker+64>) at ../../mono/utils/atomic.h:398
-6  0x002f29a0 in COUNTER_READ () at threadpool-worker-default.c:194
-7  0x002f3320 in worker_park () at threadpool-worker-default.c:426
-8  0x002f3774 in worker_thread (unused=0x0) at threadpool-worker-default.c:488
-9  0x002e66b0 in start_wrapper_internal (start_info=0x0, stack_ptr=0xb4b00000) at threads.c:982
-10 0x002e6894 in start_wrapper (data=0x5a8f38) at threads.c:1044
-11 0xb6de31a8 in start_thread () from /lib/arm-linux-gnueabi/libpthread.so.0
-12 0xb6d3a1bc in ?? () from /lib/arm-linux-gnueabi/libc.so.6
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Thread 4 (Thread 0xb40ff440 (LWP 10198)):
-0  0xb6deb56c in __lll_lock_wait () from /lib/arm-linux-gnueabi/libpthread.so.0
-1  0xb6de584c in pthread_mutex_lock () from /lib/arm-linux-gnueabi/libpthread.so.0
-2  0x00440e6c in InterlockedCompareExchange64 (dest=0x559868 <gc_stats+8>, exch=2855648, comp=2844091) at atomic.c:570
-3  0x0039bdcc in InterlockedAdd64 (dest=0x559868 <gc_stats+8>, add=11557) at ../../mono/utils/atomic.h:392
-4  0x003a1b50 in collect_nursery (reason=0x5083f4 "Nursery full", is_overflow=0, unpin_queue=0x0) at sgen-gc.c:1865
-5  0x003a3794 in sgen_perform_collection (requested_size=4096, generation_to_collect=0, reason=0x5083f4 "Nursery full", wait_to_finish=0, stw=1) at sgen-gc.c:2539
-6  0x003a35f0 in sgen_ensure_free_space (size=4096, generation=0) at sgen-gc.c:2505
-7  0x00389db0 in sgen_alloc_obj_nolock (vtable=0xb4d174d0, size=64) at sgen-alloc.c:256
-8  0x0036e330 in mono_gc_alloc_vector (vtable=0xb4d174d0, size=64, max_length=12) at sgen-mono.c:1743
-9  0xb6c16a38 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
```

fixes https://bugzilla.xamarin.com/show_bug.cgi?id=59039