Hrrmm... gnuconfig has alreaded added linux-android* upstream for
their system types in config.sub but using 'android' as a descriptor
for the libc really wouldn't make sense if it wasn't an Android
system.

It would probably be prudent to add linux-android* | linux-bionic* ...
there are a few significant differences. I guess the main
differentiators would be FHS (android prefixes everything with
/system), support for /etc/passwd, /etc/group, /etc/resolv.conf,
crypt(3), getpwnam(3), getgrnam(3), and essentially any other missing
feature that people might want to add in the future.

They also don't have an entry in config.guess for LIBC=android (or
LIBC=bionic). Something like this would work.

...
        # ifdef __BIONIC__
        # ifdef __ANDROID__
        LIBC=android
        # else
        LIBC=bionic
        # endif
        # else
        LIBC=gnu
        # endif
...

I'll add a gnuconfig revision with those changes in my overlay.

To me, it just makes sense to differentiate this way... of should
still be possible to build an Android toolchain, so I'll add
IUSE=android to the bionic ebuild. The bionic ebuild is otherwise
done, but I still have to add something for
crosscompile_opts_headers-only before it works with crossdev.

Cheers,

C