Rename ANDROIDEABI to Android.

Most of the code guarded with ANDROIDEABI are not
ARM-specific, and having no relation with arm-eabi.
Thus, it will be more natural to call this
environment "Android" instead of "ANDROIDEABI".

Note: We are not using ANDROID because several projects
are using "-DANDROID" as the conditional compilation
flag.

llvm-svn: 163087