Hello!
(I’m very new to Juce, trying to do my first Juce project.)
Just my 2 cents to the thread:
I got the same issue using Xcode 9 and Juce v 5.1.1.
I found this post which says it’s fixed.
So I downloaded Juce v 5.1.2 (sept 19, 2017), but got the same error, even after quitting Xcode.
Then I tried to clean the project (cmd-shift-K) and rebuild it (cmd-B) and everything worked fine!
Thanks a lot!