librustc: ar call fix to support android cross compile on mac

Author: yichoi

src/librustc/back/archive.rs

@@ -37,7 +37,15 @@ pub struct ArchiveRO {
 
 fn run_ar(sess: Session, args: &str, cwd: Option<&Path>,
         paths: &[&Path]) -> ProcessOutput {
-    let ar = sess.opts.ar.clone().unwrap_or_else(|| ~"ar");
+    let ar = if sess.opts.target_triple == ~"arm-linux-androideabi" {
+        match sess.opts.android_cross_path {
+            Some(ref path) => *path + "/bin/" + "arm-linux-androideabi-ar",
+            None => ~"arm-linux-androideabi-ar"
+        }
+    } else {
+        sess.opts.ar.clone().unwrap_or_else(|| ~"ar")
+    };
+
     let mut args = ~[args.to_owned()];
     let mut paths = paths.iter().map(|p| p.as_str().unwrap().to_owned());
     args.extend(&mut paths);