maint.mk suggestion for gnupload

[Eric Blake]

It was pointed out to me that for multiple years, m4's
'm4-latest.tar.XX' links were out of date at https://ftp.gnu.org/gnu/m4/
- the links were created in in 2013 when I released m4-1.4.17, but never
updated in 2016 when I released m4-1.4.18.

I managed to fix the latest links today with:

$ build-aux/gnupload --to ftp.gnu.org:m4 \
  --symlink m4-1.4.18.tar.gz m4-latest.tar.gz \
  --symlink m4-1.4.18.tar.gz.sig m4-latest.tar.gz.sig \
  --symlink m4-1.4.18.tar.bz2 m4-latest.tar.bz2 \
  --symlink m4-1.4.18.tar.bz2.sig m4-latest.tar.bz2.sig \
  --symlink m4-1.4.18.tar.xz m4-latest.tar.xz \
  --symlink m4-1.4.18.tar.xz.sig m4-latest.tar.xz.sig

but it would be a lot nicer if I didn't have to remember to do that
after the fact.  In fact, reading gnupload --help says it is as simple
as calling:

$ gnupload --to ... --symlink-regex ...

in the first place.  But --symlink-regex is not listed in the suggested
output of 'make beta' or 'make stable' from maint.mk, which is why I
missed that simpler step back in 2016, and nearly missed it again today
when I did the m4-1.4.18b beta release.  Is it worth patching maint.mk
to add --symlink-regex in the suggested gnupload instructions it generates?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org