android: Allow to use 4.7 and x86-64 toolchains if available
android: Allow to use 4.7 and x86-64 toolchains if available

Also update the CFLAGS and LDFLAGS from latest Android NDK

jackjansen/cerbero-2013,jackjansen/cerbero-2013,jackjansen/cerbero-2013,jackjansen/cerbero-2013,jackjansen/cerbero-2013