Add support for remote servers running musl

[deansheather]

sshcode pulls https://codesrv-ci.cdr.sh/latest-linux (here) which is a glibc build. There is no conditional stuff in the bash script for pulling a musl build instead, even though we do distribute musl versions of code-server.

Alpine Linux uses musl, so this will bring us closer to supporting Alpine Linux servers/containers.

[deansheather]

In the meantime, you can use the new --upload-code-server flag to upload a custom code-server binary to the remote host, which can be a musl build of code-server (or even code-server v2 preview!)