Pierre Lebeaupin on building with third party libs for iOS 6:
Word on the street is that some people have trouble doing so, however;
apparently the GM for Xcode 4.5, which Apple mandates be used for submitting
apps that use iOS 6 features, has added out of the blue a new architecture
variant called ARMv7s, and it’s causing link errors when building this slice
for app projects using third-party libraries, as those do not have an ARMv7s
slice (bit of the same issue than for ARMv6-only libraries, except more
widespread apparently). This is causing a rush to source updated version of
these dependencies or even hackish instructions (no link, because too risky)
to modify the libraries to craft an ARMv7s slice.
Check his post out for the simple fix in Xcode that will hold you over until
your third party dependencies can link with an ARMv7s build. Or, your know, use
a lib with the source instead1.