Rust target is determined by the build platform instead of the host platform

[figsoda]

riff uses target_lexicon::HOST, which is determined when riff is built, and can differ from the actual target the user runs riff with

We default to x86_64-unknown-linux-musl on linux, which differs from x86_64-unknown-linux-gnu that my cargo targets, and causes the issue mentioned in #199 (comment)

riff should try to guess what rust on the host environment targets or have a better default (gnu instead of musl) instead of using the target of the build environment