[clang] [llvm] [WebAssembly] Implement f16x8 madd and nmadd instructions. (PR #95151)

[Brendan Dahl via llvm-commits]

brendandahl wrote:

Note: I've [opened an issue](https://github.com/WebAssembly/half-precision/issues/5) about the `relaxed_` prefix and whether it should be included in the instruction name.

https://github.com/llvm/llvm-project/pull/95151