[IndVars] Set Changed if sinkUnusedInvariants changes IR. PR38863

Currently, `sinkUnusedInvariants` does not set Changed flag even if it makes
changes in the IR. There is no clear evidence that it can cause a crash, but it
looks highly suspicious and likely invalid.

Differential Revision: https://reviews.llvm.org/D51777
Reviewed By: skatkov


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341777 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed