bug#36921: texinfo: @setfilename is not mandatory

[Дилян Палаузов]

Hello,

I have a .texi file and in Makefile.am:

info_TEXINFOS = doc/z.texi

Running autoreconf -visf emits:

configure.ac:13: installing './compile'
configure.ac:7: installing './missing'
Makefile.am: installing './depcomp'
Makefile.am: error: './doc/z.texi' missing @setfilename
autoreconf: automake failed with exit status: 1

I have texinfo (or rather makeinfo) 6.6 and automake 1.16.1 (most likely 
installed from most recent git).

The texinfo manual says in node @setfilename:

“   When a '@setfilename' line is present, the Texinfo processors ignore
everything written before the '@setfilename' line.  This is why the very
first line of the file (the '\input' line) does not show up in the
output.

. . .
   '@setfilename' used to be required by the Texinfo processors, and
some other programs may still expect it to be present; for example,
Automake (*note (automake)Texinfo::).”

Please adjust automake to come forward, when @setfilename is missing, implying 
the default value.

Regards
  Dilyan