Re-export getopts so custom drivers can reference it.

Otherwise, custom drivers will have to use their own copy of `getopts`, which
won't match the types used in `CompilerCalls`.

Author: DiamondLovesYou

src/librustc_driver/lib.rs

@@ -32,7 +32,7 @@
 #![recursion_limit="256"]
 
 extern crate arena;
-extern crate getopts;
+pub extern crate getopts;
 extern crate graphviz;
 extern crate env_logger;
 #[cfg(unix)]