[clang] [llvm] [InstCombine] Strip leading zero indices from GEP (PR #155415)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

It appears that this broke our libc on GPU buildbot: https://lab.llvm.org/buildbot/#/builders/10/builds/12560
I bisected the breakage locally down to this change and reverting fixes it.
@jhuber6 for awareness. 

A failing configuration can be reproduced with `cmake -GNinja -C offload/cmake/caches/AMDGPULibcBot.cmake llvm`. Though the fail is a runtime fail afaict.

https://github.com/llvm/llvm-project/pull/155415