New notices during bootstrap

[Rik]

jwe,

I upgraded to Kubuntu 18.04 so I am suddenly using much more modern build
tools.  I'm getting a few new notices from the bootstrap procedure that I
thought deserve a look.

Notice from module strftime:
  This module is obsolete. Use module 'nstrftime' instead.

The fix for this is to use 'nstrftime' in the top-level file
bootstrap.conf.  But I don't know if this would have negative consequences
for someone with old hardware/software where gnulib has not yet defined the
module nstrftime.

Second, notice is this one

Notice from module localcharset:
  If your package's tests make use of the locale_charset() function directly or
  indirectly, you may need to define the CHARSETALIASDIR environment variable,
  so that "make check" works before "make install". In Makefile.am syntax:
  TESTS_ENVIRONMENT += @LOCALCHARSET_TESTS_ENVIRONMENT@

Octave does use the wrapped locale_charset() function directly in 4 places:

libinterp/corefcn/strfns.cc:760:    = (tmp.empty () ?
octave_locale_charset_wrapper () : tmp.c_str ());
libinterp/corefcn/strfns.cc:812:    = (tmp.empty () ?
octave_locale_charset_wrapper () : tmp.c_str ());
libinterp/corefcn/input.cc:539:              ?
octave_locale_charset_wrapper () : m_mfile_encoding;
libinterp/corefcn/input.cc:1121:         ? octave_locale_charset_wrapper ()
: mfile_encoding);

I don't whether this is a problem or not.

Third thing,

Don't forget to
  - mention "-I m4" in ACLOCAL_AMFLAGS in Makefile.am,

I don't see that we are adding '-I m4' anywhere.  On the other hand, it
seems to be getting included anyways.

running: AUTOPOINT=true LIBTOOLIZE=true autoreconf --verbose --install
--force -I m4  --no-recursive

Do you have an opinion on any of these recommendations?

--Rik