bpo-36611: Disable serialno field of debug memory allocators (#12796)

Omit serialno field from debug hooks on Python memory allocators to
reduce the memory footprint by 5%.

Enable tracemalloc to get the traceback where a memory block has been
allocated when a fatal memory error is logged to decide where to put
a breakpoint.

Compile Python with PYMEM_DEBUG_SERIALNO defined to get back the
field.