Roc linker library base setup

linker/src/main.rs

@@ -0,0 +1,17 @@
+use roc_linker::{build_app, preprocess, CMD_PREPROCESS, CMD_SURGERY};
+use std::io;
+
+fn main() -> io::Result<()> {
+    let matches = build_app().get_matches();
+
+    let exit_code = match matches.subcommand_name() {
+        None => Ok::<i32, io::Error>(-1),
+        Some(CMD_PREPROCESS) => {
+            preprocess()?;
+            Ok(0)
+        }
+        Some(CMD_SURGERY) => Ok(0),
+        _ => unreachable!(),
+    }?;
+    std::process::exit(exit_code);
+}