android-config.h

This patch adds an android-config.h configuration file that matches the
Android toolchain configuration.

It also includes an implementation of getsubopt, with the strchrnul
dependency, since the Android toolchain does not provide this
functionality.

Signed-off-by: Hans-Christian Egtvedt <hegtvedt@cisco.com>
[hans.verkuil@cisco.com: made functions inline]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>