[NFC] Pre-calculate function IR counts in size remarks.

[NFC] Pre-calculate function IR counts in size remarks.

Size remarks are slow due to lots of recalculation of the module.

Pre-calculate the module size and initial function size for a remark. Use
deltas calculated using the less-expensive function IR count to update the
module counts for Function passes.

1/6

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341245 91177308-0d34-0410-b5e6-96231b3b80d8