[llvm] [GISel] Add support for scalable vectors in getLCMType (PR #80306)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

G_UNMERGE_VALUES, G_MERGE_VALUES, and G_BUILD_VECTOR only work with fixed length vectors. Is the root cause of your crash somewhere else?

https://github.com/llvm/llvm-project/pull/80306