Facebook platform support is not detected by the editor hence the user is not able to make builds for Facebook platform.

Steps to reproduce:

1. Install Unity along with the Facebook support.
2. Launch the editor and go to -> File -> Build Settings -> Facebook.
3. Observe that the Facebook SDK is not detected by the editor and user is not able to make builds for Facebook platform.

Reproducible on :2018.3.0a8, 2018.3.0a1 , 2018.2.0f2

Working Fine on: 2018.2.0b7

Environment:
Occurs only on Mac OS