[NewPassManager] Resolve assertion in CGSCCPassManager when CallCounts change.

Summary:
If the CallCounts change after an iteration of the DevirtSCCRepeatedPass, this is not reflected in the local CallCounts structure triggering the assertion checking the before/after sizes.
Since it is valid for the size to change and this only uses the CallCounts for the devirtualizing heuristic, keep a <Function*, CallCount> map instead, and make the devirtualizing decision using the counts for the functions that exist both before and after the pass.

Resolves PR42726.

Reviewers: chandlerc

Subscribers: mehdi_amini, jlebar, sanjoy.google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65621

llvm-svn: 367703