Fix building with iOS 9 beta SDK

configure.sh was setting some Mac OS X options for iOS targets, which
confuses the iOS 9 beta SDK in Xcode 7 when linking libraries.

Additionally, old armv6 media extensions were being enabled on iOS
when they're not needed (we always have Neon since iOS 6). These
broke on iOS 9 SDK which no longer assembles those instructions.

Change-Id: I4e4d2722392ead3382ce96289c03ef1e489799d6