Add support for MIDL include directories

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

Index: test/win/idl-includedirs/subdir/foo.idl
diff --git a/test/win/idl-excluded/bad.idl b/test/win/idl-includedirs/subdir/foo.idl
similarity index 51%
copy from test/win/idl-excluded/bad.idl
copy to test/win/idl-includedirs/subdir/foo.idl
index 38554e96350a03377a5b9fcb20d95b2fe465c033..c8c65b9be6d18b70bf82350fe1b0ec910d383ee1 100644
--- a/test/win/idl-excluded/bad.idl
+++ b/test/win/idl-includedirs/subdir/foo.idl
@@ -2,5 +2,13 @@
 // 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";
+import "bar.idl";
+
+[
+  object,
+  uuid(9C1100DD-51D4-4827-AE9F-3B8FAC4AED72),
+]
+interface Foo : IUnknown {
+  HRESULT FooFunction(Bar* bar);
+};