Fix building on Alpine

[yuvald-sweet-security]

Hey,

The current version on main doesn't build on Alpine linux, failing with the error:

cannot produce proc-macro for `clap_derive v4.5.49` as the target `x86_64-unknown-linux-musl` does not support these crate types

Researching a little into this issue (one, two) seems to point to the fact that proc-macro crates cannot be compiled statically. This is not usually a problem because proc-macro crates are built to the host's target, and I assume your hosts are all x86_64-unknown-linux-gnu, and thus they don't get the target.'cfg(target_env = "musl")' clause applied to them even when cross-compiling to musl. However, when building on Alpine, the host's target is in fact musl and cargo tries to statically link proc-macro creates (and build scripts).

I am not sure if your CI somehow relies on this clause - to the best of my knowledge, cross-compiling musl binaries on non-musl systems (e.g. running cargo build --target x86_64-unknown-linux-musl on a Debian machine) already uses static linking by default, and thus explicitly specifying +crt-static here should be redundant. However, if you do need to somehow pass -C target-feature=+crt-static explicitly, you should do this in the CI pipeline where it is required and not in Cargo's global config.toml (note that when cross compiling with --target and passing custom rustflags at the same time, Cargo has a useful feature where it passes these rustflags only to binaries targeting the destination architecture, and not to host-triplet targets, thus preventing breakage of this sort in that case).

[Jake-Shadle]

Thanks!