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

[Damien Miller]

On Sun, 18 Apr 2021, Michael Forney 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).

I actually have a few workflows that run make against the Makefile.in
(e.g. generating cat format manpages as part of release) and these
break with @DEPEND@ on it's own, uncommented line. I'll need to adjust
these before merging this.

It's unfortunate that AC_SUBST_FILE has the whole-line restriction
whereas AC_SUBST does not :(

-d