Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

Versions.

Angular CLI: 1.5.0
Node: 8.7.0
OS: darwin x64
Angular: 5.0.0

Repro steps.

We have a the following folder structure in a git mono-repo

/api (Express Node App)
/model (NPM package using NPM Link, contains mostly typescript interfaces)
/web (Angular)

When using Angular 4.46 and Angular CLI 1.5.rc2 and we were able to make reference to the interfaces defined in the model folder using npm link and using the following example
import { entity } @app/model

We use ng serve to start the app.

After upgrading Angular to V5 and Angular CLI to 1.5.0 we now get the following error -

The log given by the failure.

Module build failed: Error: /Users/thaoula/Projects/platform/model/index.ts is not part of the compilation. Please make sure it is in your tsconfig via the 'files' or 'include' property.

The occurs for JIT and AOT builds.
Running TSC does not result in in errors.

Desired functionality.

Would like be able to build the app using Angular 5

Thanks,
Tarek