[CallSiteSplitting] Don't let debug intrinsics affect optimizations

Summary:
This solves PR35616.

We don't want the compiler to generate different code when we compile
with/without -g, so we now ignore debug intrinsics when determining if
the optimization can trigger or not.

Reviewers: junbuml

Subscribers: davide, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D41068

llvm-svn: 320460