[llvm] [GlobalISel] Combine away G_UNMERGE(G_IMPLICITDEF). (PR #119183)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

It also in the standard combiner:
https://github.com/llvm/llvm-project/blob/9ddc31d060a05b1706b8a9f26323ad1ed1e21a82/llvm/include/llvm/Target/GlobalISel/Combine.td#L828

https://github.com/llvm/llvm-project/pull/119183