[llvm] [SeparateConstOffsetFromGEP] Update splitGEP to handle case where including base offset results in an offset that's too large (PR #177653)

[Adel Ejjeh via llvm-commits]

adelejjeh wrote:

@arsenm Unless you think we need to wait for other reviews, can you merge this PR for me please? I don't have access.

https://github.com/llvm/llvm-project/pull/177653