Target maintainers: doc/install.texi love and care

[Gerald Pfeifer]

I noticed that the target-specific sections in doc/install.texi
need a little lover and care.  It would be great could you have
a look and streamline/update before the GCC 7 release.

Thanks!


Also, I'm offering help around one particular aspect I noticed:

References to dependencies on really, really old versions of
binutils (talking 10+ years here) which I think we can remove.
Let me follow-up with some of you with concrete suggestions 
around that.

Gerald