iOS xCode5 Unsupported compiler 'com.apple.compilers.llvmgcc42' error when compiler set to LLVM 5.0

I'm trying to open one of my older projects, that was built using iOS 6.0. The project used to compile fine, but when opened under xCode 5, I get this cryptic error message.

Unsupported compiler 'com.apple.compilers.llvmgcc42' selected for architecture 'armv7'
Unable to determine concrete GCC compiler for file /Users/alexanderstone/Desktop/Development/RestKit/Vendor/NXJSON/NSError+Extensions.m of type sourcecode.c.objc.
Unable to determine concrete GCC compiler for file /Users/alexanderstone/Desktop/Development/RestKit/Vendor/NXJSON/NXDebug.m of type sourcecode.c.objc.
Unable to determine concrete GCC compiler for file /Users/alexanderstone/Desktop/Development/RestKit/Vendor/NXJSON/NXJsonParser.m of type sourcecode.c.objc.
Unable to determine concrete GCC compiler for file /Users/alexanderstone/Desktop/Development/RestKit/Vendor/NXJSON/NXJsonSerializer.m of type sourcecode.c.objc.

I've checked both project build settings, and they appear correct - LLVM 5.0 is selected as compiler for both.

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Additionally, I checked the .m files that compiler complains about, and do not see any reference to GCC there. There are some ASSERT() and other macros, but I don't know if they are compiler-specific.

How can I resolve the llvmgcc4.2 compiler missing in xCode 5, when all subprojects appear to be set to llvm5.0?

Solution

Found this similar question. For me the solution was to go to Editor>Validate Project settings for both the child and the Restkit projects.