I would like to build fat binaries with x86_64 and i386 architecture support.  I've tried passing the flag
    -DCMAKE_OSX_ARCHITECTURES=x86_64;i386
to cmake, but it appears that flag isn't being carried down to the building of libtinyxml.a and libyaml-cpp.a:

    ld: warning: in ../../ext/dist/lib/libtinyxml.a, file was built for unsupported file format which is not the architecture being linked (i386)
    ld: warning: in ../../ext/dist/lib/libyaml-cpp.a, file was built for unsupported file format which is not the architecture being linked (i386)

(Note:  I get the same errors if I try to build for just i386.)

Does anyone have any suggestions for what I can try?  Thanks!