Xcode 4.1 fatal error: stdlib modified since the precompiled header was built

Question

Building an iPhone app, using:

• Xcode 4.1
• Base SDK iOS 4.3
• Apple LLVM Compiler 2.1

I have started getting the following error

Answer 1

I thought I would add a separate answer rather than a comment to Cryptognome's answer, because it is in fact a different solution when the issue comes from running xcodebuild. Like Cryptognome, I had the error come up with the command-line tool xcodebuild. As an alternative to manually going into the /var subfolders, I found that I could set my own cache for the shared PCH, which you can do by setting the environment variable SHARED_PRECOMPS_DIR, e.g as follows

xcodebuild -target Foo -configuration Release SHARED_PRECOMPS_DIR=/tmp/foo/SharedPCH

This way, I never get the error in automatic builds.

Note in the above command, I would also typically set the OBJROOT and SYMROOT env var to build also in /tmp. At the end, I clean things up.