[PATCH] Use AC_SUBST_FILE to replace @DEPEND@ with contents of .depend

[Michael Forney]

On 2021-04-18, Michael Forney <mforney at mforney.org> wrote:
> AC_SUBST_FILE[0] is similar to AC_SUBST, but instead of replacing
> a variable with its value, it replaces a variable with the contents
> of the file named by the value. This is exactly what we want in
> order to insert the contents of .depend at the end of the Makefile.
>
> Using AC_SUBST for this purpose poses some problems if $as_echo
> involves running an external command (i.e. printf is not built-in),
> in which case the size of .depend may exceed the operating system's
> argument size limit. In particular, since autoconf 2.70, $as_echo
> no longer uses `print -r` on ksh shells[1], causing the following
> message when creating config.log on Linux with oksh:
>
>   ./configure: printf: Argument list too long
>
> AC_SUBST_FILE requires the substitution string to be on its own
> line, so drop the unneeded leading comment (the first line of .depend
> has a '#' of its own).
>
> [0]
> https://www.gnu.org/software/autoconf/manual/html_node/Setting-Output-Variables.html
> [1]
> http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=2b59b6f8a79b8bf77e178ff4e5aa0ede433d39cf;hp=bea5177adc0c924fe7483509a5e38a6d49319fcb

Ping on this patch.