Add specific musl host triple architecture
Add specific musl host triple architecture

This allows us to ship separate agent builds for GNU and musl builds.
Hopefully solving the DNS timeouts issue for good:
https://docs.appsignal.com/support/known-issues.html#dns-timeouts

The musl-compatible agent can be force installed with the
`APPSIGNAL_BUILD_FOR_MUSL` environment variable.

Override with `export APPSIGNAL_BUILD_FOR_MUSL=1` before calling `mix
{task}` if this doesn't work automatically.

appsignal/appsignal-elixir,appsignal/appsignal-elixir,appsignal/appsignal-elixir,appsignal/appsignal-elixir