[llvm] GlobalISel/Combiner: Fix building G_CONSTANT for fp extended LLT (PR #196397)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

This looks like it makes perormance quite a bit worse? It should not really be necessary for a G_CONSTANT to have a integer type.

https://github.com/llvm/llvm-project/pull/196397