[bug#67268] [PATCH] texinfo: add pointer about combining tests

    very extensive "Portable Shell Programming" chapter:
    https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.71/html_node/Portable-Shell.html

I know. The Autoconf manual already describes this issue in detail.
The point of the brief mention in the Automake manual is because it is
precisely the place and the problem that are rather likely to come up
in practice.

I see I failed to link to the Autoconf node, though. I'll add that. -k