iOS clang: error: linker command failed with exit code 1 (use -v to see invocation)

Here is what I did after spending 2 days trying to fix this.

1. Clean the Build

Menu Bar → Product → Clean

1. Delete Derived Data

2. Delete Xcode Preferences
   in terminal
   
   defaults delete com.apple.dt.Xcode
   

3. make sure your build setting are on new build setting instead of legacy build setting.
   I can't be sure what worked exactly and what happened in the background, but it worked for me.