Fix a hanging build with non-GNU make

[Bruno Haible]

On Solaris, with Solaris 'make', the build hangs here:

Making all in doc
/opt/csw/bin/gsed -n -e 's/^\* \([^:]*\)::.*/\1/p'  | /opt/csw/bin/gsed -e 's| 
|/|g' \
          > nodelist

Of course, a 'gsed' invocation with no file arguments reads from stdin and
thus hangs. The problem is the use of '$<', which is only allowed in
suffix rules (called "inference rules" in POSIX), per
<https://pubs.opengroup.org/onlinepubs/9699919799/utilities/make.html>.

See also the Autoconf manual
<https://www.gnu.org/software/autoconf/manual/autoconf-2.70/html_node/_0024_003c-in-Ordinary-Make-Rules.html>

Here is a proposed fix.

0001-Fix-a-hanging-build-with-non-GNU-make.patch
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