I intended to point out that it's potential bug with Xcode itself.
Here is the gist of the mentioned link:
The error was caused by a name conflict between my project name, GoogleSignIn, and the package for Google's sign-in, GoogleSignIn from https://github.com/google/GoogleSignIn-iOS.
I fixed this by re-creating my project with a different name, like MyGoogleSignIn.
Error message
Multiple commands produce '.../Library/Developer/Xcode/DerivedData/GoogleSignIn-hjk
Topic:
Developer Tools & Services
SubTopic:
Xcode