Add option to use musl builds

[prabirshrestha]

Run moonrepo/setup-toolchain@v0.4.1
  with:
    auto-install: true
    cache: true
    moon-version: 1.35.3
    proto-version: 0.48.1
  env:
    RUST_BACKTRACE: 1
    version: 0.6.31
    CARGO_INCREMENTAL: 0
    CARGO_TERM_COLOR: always
Added /root/.proto/shims and /root/.proto/bin to PATH
Installing `proto` globally
Downloading installation script
Downloaded script to /root/.proto/temp/proto.sh
Executing installation script
Error: Error: Command failed with exit code 1: /root/.proto/temp/proto.sh 0.48.1
#=#=#                                                                         
##O#- #                                                                       

                                                                           0.2%
######################################################################## 100.0%
/root/.proto/bin/proto: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /root/.proto/bin/proto)
/root/.proto/bin/proto: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.33' not found (required by /root/.proto/bin/proto)
/root/.proto/bin/proto: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by /root/.proto/bin/proto)

or might be it should default to musl for linux builds for both proto and moon?

[milesj]

Right now the musl logic is hard coded in the install script: https://github.com/moonrepo/moon/blob/master/website/static/install/proto.sh#L71

I'll have to add an env var or something.