If you’ve recently upgraded to Xcode and your build failed with the following error:
error: PCH file built from a different branch ((clang-425.0.24)) than the compiler ((clang-425.0.27))
Solution 1: Go to your menu bar and select Product | Clean and try building your package again.
This occurs because Xcode is confused as to where all of your Precompiled Headers are.
Solution 2: If the above doesn’t work, hold the Option Key down when clicking on Product and you’ll see Clean Build Folder instead.
Solution 3: In a really dire situation you’ll have to go and delete the SharedPrecompiledFolders that’s in your log. Typically this will occur if you’re using a command line driven build like I was. Look for this in your log:
Delete the folder (not just the contents) and rebuild your product.