[PassTiming] reporting time-passes separately for multiple pass instances of the same pass

Summary:
Refactoring done by rL340872 accidentally appeared to be non-NFC, changing the way how
multiple instances of the same pass are handled - aggregation of results by PassName
forced data for multiple instances to be merged together and reported as one line.

Getting back to creating/reporting timers per pass instance.
Reporting was a bit enhanced by counting pass instances and adding #<num> suffix
to the pass description. Note that it is instances that are being counted,
not invocations of them.

time-passes test updated to account for multiple passes being run.

Reviewers: paquette, jhenderson, MatzeB, skatkov

Reviewed By: skatkov

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D51535

llvm-svn: 341346