We could allocate chunks larger than 4GB, but did our size-accounting in 32-bit
values. This could lead to spurious warnings, inaccurate accounting, and, in
theory, data loss.

Affected: 64-bit platforms. Debug-build (with safemalloc). At least one buffer
larger than 4GB. For potential data loss, a re-alloc on such a buffer would be
necessary.


mysys/my_static.c:
  Make memory-accounting 64-bit safe.
mysys/my_static.h:
  Make memory-accounting 64-bit safe.
  Move in struct for better alignment when 64-bit.