[llvm] [GlobalIsel] Combine G_SELECT (PR #74845)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

This check will fail once scalable vector splats get merged:

https://github.com/llvm/llvm-project/blob/bfebadc8c392fc3bc8cbd54af735a006f50a5d8c/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp#L317

https://github.com/llvm/llvm-project/pull/74845