suppress warnings about unused things

Signed-off-by: xermicus <cyrill@parity.io>

crates/lld-sys/Cargo.toml

@@ -11,4 +11,10 @@ build = "build.rs"
 libc = { workspace = true }
 
 [build-dependencies]
-cc = { workspace = true }
+cc = { workspace = true }
+
+[target.aarch64-apple-darwin]
+rustflags = [
+  "-C", "link-arg=-undefined",
+  "-C", "link-arg=dynamic_lookup",
+]