Android build target resolve

Work around the build name issues by instead
manually adding the build target for android
builds using '-DOS=android'

This additionally resolves problems caused by the
OS variable being rewritten from "android" to
"linux" in gyp.
This causes errors, as real-time support (-lrt)
and pthread support (-lpthread) is not available
in the android NDK toolchain as libraries.
The functions present in these libraries are
included automatically during the build instead
during the android compilation process.