[DebugInfo] Allow bundled calls in the MIR's call site info

Summary:
Extend the MIR parser and writer so that the call site information can
refer to calls that are bundled.

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

Reviewed By: aprantl

Subscribers: arsenm, hiraditya, llvm-commits

Tags: #debug-info, #llvm

Differential Revision: https://reviews.llvm.org/D66145

llvm-svn: 369256