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OS X version 10.9.4.
$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.3.0
Thread model: posix
This is the warning:
...
gcc -bundle -undefined dynamic_lookup build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/_ctypes.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/callbacks.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/callproc.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/stgdict.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/cfield.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/malloc_closure.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/darwin/dlfcn_simple.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/ffi.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/x86/darwin64.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/x86/x86-darwin.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/x86/x86-ffi_darwin.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/x86/x86-ffi64.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/powerpc/ppc-darwin.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/powerpc/ppc-darwin_closure.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/powerpc/ppc-ffi_darwin.o build/temp.macosx-10.9-x86_64-3.5-pydebug/Users/sky/Code/python/cpython/Modules/_ctypes/libffi_osx/powerpc/ppc64-darwin_closure.o -L/usr/local/lib -o build/lib.macosx-10.9-x86_64-3.5-pydebug/_ctypes.so
ld: warning: could not create compact unwind for _ffi_call_unix64: does not use RBP or RSP based frame
Python build finished successfully!

That warning has been around for some time. The question is: is it something to be concerned about? I don't know of any ctypes test failures on OS X. There have been various discussions of the warning in other (non-Python) contexts, for example, https://sourceware.org/ml/libffi-discuss/2011/msg00109.html.