alpine cannot build rust agent

[yyyeerbo]

alpine doesn't support x86_64-unknown-linux-gnu

It only support x86_64-unknown-linux-musl. Even worse,

it doesn't support proc-macro, which is needed for serde_derive

[liubin]

rust-lang/rust#69519

[liubin]

May be fixed by 1.44 rust-lang/rust#40174 (comment) and rust-lang/rust#40174 (comment)

[liubin]

I have tried this and verified that 1.45 has resolved this issue.

$ docker run -it --rm -v `pwd`/kata-containers:/kc  rust:1.45.2-alpine3.12 sh
# cd /kc
# apk add --no-cache musl-dev
# cargo build