Add missing Debuginfo to PDB debug file on windows.

Set Arg0 and CommandLineArgs in MCTargetoptions so LLVM outputs correct CL and CMD in LF_DEBUGINFO instead of empty/invalid values.

compiler/rustc_interface/src/tests.rs

@@ -68,6 +68,7 @@ fn mk_session(handler: &mut EarlyErrorHandler, matches: getopts::Matches) -> (Se
         None,
         "",
         None,
+        Default::default(),
     );
     (sess, cfg)
 }