compiletest: `//@ needs-dynamic-linking` should rule out musl since it supports neither dylibs nor cdylibs

[jieyouxu]

Noticed in #130860. Should double-check the detection mechanism to determine why we thought musl targets supported dynamic linking in the first place.

[jieyouxu]

cf. #132309

[bjorn3]

Musl fully supports dylibs. We are statically linking musl libc by default however, which is not compatible with dylibs. Using -Ctarget-features=-crt-static will link musl dynamically, making dylibs work just fine. We should be migrating to dynamically linking musl in the future to better work with distros that use musl as their libc implementation, but nobody has been working on implementing this.

[jieyouxu]

Closing this because it's wrong.