Tweak for no-libio-install

[Benjamin Kosnik]

> If src/Makefile decides that it doesn't need to install any libio
> files, it dies with a shell syntax error.  Here's a (semi-tested) patch.

Won't work for xcompiles. Sorry. No can do.

More to the point, a linux build doesn't require the build or install of
libio related stuff--I tested this and it works for me. Still works, as a
matter of fact.

Why is it not working for you, or am I not understanding the problem?

I didn't test with the egcs/v-3 combo tho. Maybe that's the
problem...anyway, please clarify, or tell me how to reproduce...

-benjamin