libselinux and SELinux support for coreutils

[kyufie]

This PR introduces a new library (libandroid-selinux) for basic SELinux functionality.
Along with that, I've also added SELinux support to coreutils.
chcon and ls -Z seems to be working.
I still haven't done a thorough testing just yet so it might still have a few catch, but that should not break existing functionalities.

[kyufie]

The added SELinux feature seems to be working just fine except for the ability to set default context type, but that's expected considering the library itself have the feature disabled when built for Android.
The non-SELinux related operations seems unaffected by this change.

Here's the list of the progams I've tested:

• chcon
• copy
• copy
• id
• install
• ls
• mkdir
• mkfifo
• mknod
• runcon
• stat

[truboxl]

Ok LGTM I will help merge unless someone objects

[kyufie]

Many thanks.

[truboxl]

I do have concern though whether some build systems are stupidly enough to hardcode detect libselinux.so.1 and porting become a hassle later on (many patches).

Should be rectified somewhat using modified pc.in files which can be added later. And in the worst scenario can change the soname back which should be done as early as possible.

Not to say I don't like libandroid-selinux since it can avoid conflict with system libselinux and we got a few instances of that case in the past. I will merge in as is in a few hours.

[truboxl]

Thanks for the hard work!