Append to the ActiveTimers std::vector before looking at the timer instead

Append to the ActiveTimers std::vector before looking at the timer instead
of after, so that any reallocation it does doesn't get counted for the pass
being timed.  This probably doesn't account for a timing discrepancy I was
looking into, but I'm fixing it anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52693 91177308-0d34-0410-b5e6-96231b3b80d8