[PM] Move the collection of call sites to a more appropriate place

inside of `InlineFunction`. Prior to this, call instructions are
specifically being rewritten and replaced within the inlined region,
invalidating some of the call sites.

Several of these regions are using the same technique to walk the
inlined region so this seems clearly safe up to this point.

I've also added a short circuit to the scan for call sites based on what
other code is doing.

With this, the most common crash I've found in the new inliner code is
fixed. I've turned it on for another test case that covers this
scenario.

I'll make my way through most of the other inliner test cases
just to get some easy coverage next.

llvm-svn: 290562