driver: perform stripping before and after macro expansion.

This allows macros to both be conditionally defined, and expand
to items with #[cfg]'s.

src/test/run-pass/cfg-macros-foo.rs

@@ -0,0 +1,35 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-fast compile-flags directive doesn't work for check-fast
+// compile-flags: --cfg foo
+
+// check that cfg correctly chooses between the macro impls (see also
+// cfg-macros-notfoo.rs)
+
+#[cfg(foo)]
+#[macro_escape]
+mod foo {
+    macro_rules! bar {
+        () => { true }
+    }
+}
+
+#[cfg(not(foo))]
+#[macro_escape]
+mod foo {
+    macro_rules! bar {
+        () => { false }
+    }
+}
+
+fn main() {
+    assert!(bar!())
+}

src/test/run-pass/cfg-macros-notfoo.rs

@@ -0,0 +1,35 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-fast compile-flags directive doesn't work for check-fast
+// compile-flags:
+
+// check that cfg correctly chooses between the macro impls (see also
+// cfg-macros-foo.rs)
+
+#[cfg(foo)]
+#[macro_escape]
+mod foo {
+    macro_rules! bar {
+        () => { true }
+    }
+}
+
+#[cfg(not(foo))]
+#[macro_escape]
+mod foo {
+    macro_rules! bar {
+        () => { false }
+    }
+}
+
+fn main() {
+    assert!(!bar!())
+}