I'm guessing that extern_c is a compiler directive for the module map saying it is referencing functions from C++ that were written in the C language (different call frame structure).
The LLVM portion of the CLANG compiler is probably having a version mismatch.
http://clang.llvm.org/docs/Modules.html#module-maps
Try a command line $ clang -v
You may have to verify the compiler library version
xcode->preferences->locations->command line tools.
Ultimately you will want to clear this up so your stack frames match the arguments and your not referencing a C language function.