Make "all" depend on "info"

Make "all" depend on "info"

I've broken "make info" a couple of times now, because I sometimes
forget to run "make info" after modifying a Texinfo file.

I don't know why gdb's "make all" doesn't build the info pages.  I
suspect this was some Cygnus-local oddity back in the day.

This patch changes doc/Makefile.in so that the info pages are built by
"make all".  As a point of reference, Automake has essentially always
worked this way.  According to the Automake manual (I didn't
double-check) this is required by the GNU coding standards.

The first time I sent this patch, I mentioned that I wanted to look
into some existing bugs in bugzilla about missing "makeinfo".
However, today I tried and I discovered that BFD requires makeinfo,
and builds its info file as part of "all".  So, I think this change
doesn't worsen the situation for users in any way, and can simply go
in.

gdb/doc/ChangeLog
2019-04-07  Tom Tromey  <tom@tromey.com>

	* Makefile.in (all): Depend on "info".