[llvm-branch-commits] [llvm] [LoongArch] Optimize general fp build_vector lowering (PR #149486)

[Lu Weining via llvm-branch-commits]

https://github.com/SixWeining approved this pull request.

AArch64 has similar logic.
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp#L15259-L15286

https://github.com/llvm/llvm-project/pull/149486