support android build and glue

Fixed according to your advice.
Is it fine?

As Ilyong's comment, actually It is needed android-glue in android.
we need to separate the each platforms in makefile.in?
we added linking libandroid-glut.a on making librustglut.so. 
It will be fine at linux or macos build.
however it seems not obious for other people so that it may causes some confusion.
I don't know what is better. shorter code is better or clear code is better..

Let me know your opinion, and we will be very appreciated.