Add support for building on Alpine targets (musl)

[Elinvynia]

Hello! I have been messing around with trying to get the binary build statically linked, and there are two major roadblocks:

On: rust:alpine
darling_macro will refuse to compile while building on alpine with a musl target.

On: clux/muslrust
sass-rs will refuse to compile while building on debian with a musl target.

I've looked into compass-rs/sass-rs#30 and tried tweaking various other things, but nothing worked.

Thanks in advance!

[epage]

darling_macro will refuse to compile while building on alpine with a musl target.

Thats strange. Have you opened an issue with them?

sass-rs will refuse to compile while building on debian with a musl target.

We have sass configured as a Rust feature. You could build with no default features and then re-enable the ones you want / work.

[Elinvynia]

There is TedDriggs/darling#94, the repo had its last activity 2 months ago. The reason I asked here is in case anyone had some experience trying to compile cobalt with SASS enabled on musl.

I've managed to get it working without the SASS feature using this Dockerfile: https://github.com/Elinvynia/blog/blob/master/Dockerfile but I figured it would be nice to have it enabled.