[DebugInfo] Remove call sites when eliminating unreachable blocks

[DebugInfo] Remove call sites when eliminating unreachable blocks

Summary:
When eliminating an unreachable block we must remove any call site
information for calls residing in the block.

This was originally found on a downstream target, and the attached x86
test case was produced by hand-modifying some MIR.

Reviewers: aprantl, asowda, NikolaPrica, djtodoro, ivanbaev, vsk

Reviewed By: NikolaPrica, vsk

Subscribers: vsk, hiraditya, llvm-commits

Tags: #debug-info, #llvm

Differential Revision: https://reviews.llvm.org/D64500

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@368566 91177308-0d34-0410-b5e6-96231b3b80d8