[llvm] [X86][GlobalISel] Support G_FADD, G_FSUB, G_FMUL, G_FDIV (PR #87339)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

2 nits: AArch64 has `.moreElementsToNextPow2(0);` and could you try non-power-of-2 length vectors to stress you legalizer.

https://github.com/llvm/llvm-project/pull/87339