[llvm] [AArch64][GlobalISel] Check unmergeSrc is a vector in matchCombineBuildUnmerge (PR #168692)

[Nathan Corbyn via llvm-commits]

https://github.com/cofibrant requested changes to this pull request.

Could you add the reproducer from https://github.com/llvm/llvm-project/issues/168495 as a test case?

https://github.com/llvm/llvm-project/pull/168692