missing quotes in gcc/Makefile.in (stmp-fixinc)

[DJ Delorie]

> Or if you run out of environment space...

I suppose that's true, but given how much we take for granted in the
builds already, we'd have to go through a lot to guarantee that every
command work exactly right.  Consider what "make install" goes
through.

I'm not saying that's *good*, but it's good enough, and if/as people
actually encounter problems, we nibble away at it.