[TailRecursionElimination] Skip debug intrinsics.

Summary:
I think we do not need to analyze debug intrinsics here, as they should
not impact codegen. This has 2 benefits: 1) slightly less work to do and
2) avoiding generating optimization remarks for converting calls to
debug intrinsics to tail calls, which are not really helpful for users.

Based on work by Sander de Smalen.

Reviewers: davide, trentxintong, aprantl

Reviewed By: aprantl

Subscribers: llvm-commits, JDevlieghere

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D40440

llvm-svn: 319158