Add support for MIDL include directories

test/win/idl-includedirs/subdir/bar.idl

Index: test/win/idl-includedirs/subdir/bar.idl
diff --git a/test/win/idl-excluded/bad.idl b/test/win/idl-includedirs/subdir/bar.idl
similarity index 55%
copy from test/win/idl-excluded/bad.idl
copy to test/win/idl-includedirs/subdir/bar.idl
index 38554e96350a03377a5b9fcb20d95b2fe465c033..d4e6cbb3eb950c9441945c8d27cde364aa849b90 100644
--- a/test/win/idl-excluded/bad.idl
+++ b/test/win/idl-includedirs/subdir/bar.idl
@@ -2,5 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-This is a dummy .idl file that will trigger an error if it is not excluded from
-the build.
+import "oaidl.idl";
+
+[
+  object,
+  uuid(A03D1421-B1EC-11D0-8C3A-00C04FC31D3F),
+]
+interface Bar : IUnknown {
+  HRESULT BarFunction();
+};