[llvm] [BasicBlockUtils] Remove redundant llvm.dbg instructions after blocks to reduce compile time (PR #89069)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

The compile time impact of this change looks to be more-or-less neutral on the compile time tracker - at ReleaseLTO-g, the geomean compile time change is +0.02%. Since it looks like this solves some particularly pathological cases though it's probably worth having - so SGTM as long as @fhahn has no more comments and is happy with the current state of the patch.

https://github.com/llvm/llvm-project/pull/89069