Add support for Android

Hello. I'm going to Clang compile all f3 utilities for arm-v7a and arm64-v8a, Android 4.4+. Do I need to specify some additional flags to the compiler related to the features of these architectures and Android versions for the correct and most accurate and fast operation of the utilities? For example, `-mfpu=vfpv3`, `-mfloat-abi=hard`, `-mthumb`, `-fPIE` or `-fPIC`, minimum Android API level (19+), SELinux?