[ResetMachineFunctionPass] Add visited functions statistics info

[ResetMachineFunctionPass] Add visited functions statistics info

Adding a "NumFunctionsVisited" for collecting the visited function number.
It can be used to collect function pass rate in some tests,
the pass rate = (NumberVisited - NumberReset)/NumberVisited.
e.g. it can be used for caculating GlobalISel pass rate in Test-Suite.

Patch by Tianyang Zhu (zhutianyang)

Differential Revision: https://reviews.llvm.org/D59285

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356114 91177308-0d34-0410-b5e6-96231b3b80d8