Allow rust binaries to remove dead code

Note: we may need to add a special init function to stop linker based dead code elimination.
That or special linker commands to keep `roc_*` functions.
Currently this is working on my x86 machine without it though.

Guide here if needed on the init function:
https://stackoverflow.com/questions/43712979/how-to-export-a-symbol-from-a-rust-executable

crates/compiler/build/src/link.rs

@@ -548,7 +548,7 @@ pub fn rebuild_host(
             let rust_flags = if cfg!(windows) {
                 "-Z export-executable-symbols"
             } else {
-                "-C link-dead-code"
+                "-C link-args=-rdynamic"
             };
             cargo_cmd.env("RUSTFLAGS", rust_flags);
             cargo_cmd.args(["--bin", "host"]);