Fix nondeterministic output in local stack slot alloc pass

Fix nondeterministic output in local stack slot alloc pass

This finds all of the references to a frame index in a function, and
sorts by the offset. If multiple instructions use the same offset,
nothing was breaking the tie for sorting.

This avoids the test failures the reverted r282999 introduced.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285201 91177308-0d34-0410-b5e6-96231b3b80d8