Before this fix, the command
  SHOW ENGINE PERFORMANCE_SCHEMA STATUS
could report wrong amount of memory allocated,
when the amount of memory used exceeds 4GB.

The problem is that size computations are not done using size_t,
so that overflows do occur, truncating the results.

This fix compute memory sizes properly with size_t.

Tested manually.

No test script provided, as the script would need to allocate too much 
memory for the test.