Fix bare-metal build break

[conradgrobler]

Since Wasm support has been added to the bare-metal runtime, the build fails at link time. This is because Wasmi relies on floating point features that was not supported.

This is fixed by:

• No longer disabling SIMD: kernels disable SIMD to avoid having to backup and restore floating point registers during context switching. The bare-metal runtime will not implement user-space processes or pre-emptive threading, so this is not a consideration for us.
• Making libm implementations of fmod and fmodf available to the linker. This is done by the Rust compiler-builtins crate, but only for UEFI on the x86_64 platform (https://github.com/rust-lang/compiler-builtins/blob/master/src/math.rs#L23). Also see Link errors when compiling for i386 with +soft-float rust-lang/rust#62729

[github-actions]

Reproducibility Index:

eadcb5aab7eb4ee0d91e178868ca59a1524c4ed7a14d67ac5e99e5683d08871d  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_base
6358962ad071a3982c98296d56b6a6cf0c37e2f46cf22c4d2a2b99ed10eb4e71  ./target/x86_64-unknown-linux-musl/release/oak_functions_loader_unsafe

Reproducibility Index diff: