[llvm] [GlobalIsel] Pust cast through build vector (PR #104634)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Inside the combiner, it is a win and opens new opportunities for further simplifications on the vector lanes. In assembler, it seems to be a mix of wins and regressions. That's why I asked for more eyes.


https://github.com/llvm/llvm-project/pull/104634