XCode 7.3.1 hangs on "copying swift standard libraries"

Question

Since I have updated to XCode 7.3.1, I'm not able to run my project because it hangs on the "Copying Swift standard libraries" step (both from IDE and command line). It also crashes if I try to open the project configuration file or if I create a new Swift project.

Does anyone have idea why this is happening?

I'm running XCode on Mac mini (late 2012) with OSX 10.11.6

SOLVED
Finally solved reinstalling XCode and SDK.
Thank you all for the answers.

Answer 1

1. Open Keychain Access
2. You may find a LOT of appleid certificates (1000+ of them)
3. Delete all of those appleid certificates.

Problem solved.

Answer 2

I had this problem on Xcode Version 8.0 (8A218a) and OSX Sierra 10.12.1.

It turned out that Keychain access had been messed up with the OSX upgrade. For some reason Xcode was not surfacing the problem and was happily building but hanging on the "Copying Swift standard libraries..." leading me to do the usual fixes detailed here

In the end what fixed it was resetting the Keychain (a pain I know!) and re-creating the developer certificates. There may be a better way which is less destructive but this is how I solved it.