In texinfo, @var is for metasyntactic variables only, that is, things
that stand for other things *in the manual*. If you need a guideline,
then @var is only appropriate if you can replace the name with some
other name, say, the mathematician's favorite, x (or x1, x2, x3 ...)
and that replacement does not change the meaning of the text. Along
the same tangent, it does not make sense to mention some @var that is
not defined anywhere, e.g., as argument in a function declaration.
With that in mind, the patch below cleans up the Libtool manual, and
follows the Texinfo manual's recommendation of using lower-case @var.
OK to commit?