Include already promoted counts when computing SUM for VP.

Summary: When computing the SUM for indirect call promotion, if the callsite is already promoted in the profile, it will be promoted before ICP. In the current implementation, ICP only sees remaining counts in SUM. This may cause extra indirect call targets being promoted. This patch updates the SUM to include the counts already promoted earlier. This way we do not end up promoting too many indirect call targets.

Reviewers: tejohnson

Reviewed By: tejohnson

Subscribers: llvm-commits, sanjoy

Differential Revision: https://reviews.llvm.org/D38763

llvm-svn: 317502