Fix Makefile for FDL version fix

[Roland McGrath]

> It turns out that the texinfo.tex maintainer
> prefers the trailing white space, for editing convenience.

What does that mean???  I can't even imagine.

> So we're keeping the white space in the gnulib copy,
> and it may be better to do the same in glibc's.

We have a policy enforced by git hooks that prevents it.
So it would take special effort to get bogons into our repository.