Add test case for exported macros vs incremental compilation.

src/test/compile-fail/incr_comp_with_macro_export.rs

@@ -0,0 +1,23 @@
+// Copyright 2016 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.
+
+// compile-flags: -Zincremental=tmp/cfail-tests/incr_comp_with_macro_export
+// must-compile-successfully
+
+
+// This test case makes sure that we can compile with incremental compilation
+// enabled when there are macros exported from this crate. (See #37756)
+
+#![crate_type="rlib"]
+
+#[macro_export]
+macro_rules! some_macro {
+    ($e:expr) => ($e + 1)
+}