small bug fix for cppexp.c error messages

[Per Bothner]

Zack Weinberg <zack@wolery.cumb.org> writes:

> I'm not actually sure how portable %.*s is.  I know it's in C89, but
> was it available before then?

It is quite portable.  It was definitly in ANSI C.  I believe it
was in the original K&R book, but I'm not sure.  I haven't heard
of any system *not* supporting it.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/