Use a method to apply RustcOptGroup to getopts::Options

compiler/rustc_interface/src/tests.rs

@@ -102,7 +102,7 @@ where
 fn optgroups() -> getopts::Options {
     let mut opts = getopts::Options::new();
     for group in rustc_optgroups() {
-        (group.apply)(&mut opts);
+        group.apply(&mut opts);
     }
     return opts;
 }