Disable building the only active architecture in Lumberjack

Because we're not yet building 64-bit for our primary targets, if we tell
Lumberjack to build active architecture only with a 64-bit destination,
it'll produce a thin 64-bit binary. Ld can't statically link that into a
thin 32-bit binary (i.e. KHAThirdParty).

Test Plan:
Compile. Use `lipo -info` to verify that libCocoaLumberjack is fat.