Add 'modern-mode' command line option

	* src/emacs.c (standard_args): Add: '-m' '-modern' '--modern'
	cmd line option.

	* lisp/startup.el (command-line-1): Handle modern-mode cmd line
	option.
2 jobs for scratch/modern-mode in 21 minutes and 42 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
failed #7726
test-filenotify-gio

00:21:32

failed #7727
test-gnustep

00:21:42

 
Name Stage Failure
failed
test-gnustep Test
  SCRAPE   ./cedet/semantic/wisent ./cedet/srecode ./emacs-lisp ./emulation ...
SCRAPE ./erc ./eshell ./gnus ./image ./international ./language ./leim ...
SCRAPE ./leim/ja-dic ./leim/quail ./mail ./mh-e ./net ./nxml ./org ...
SCRAPE ./play ./progmodes ./textmodes ./url ./vc
INFO Scraping files for loaddefs.el...
INFO Scraping files for loaddefs.el...10%
INFO Scraping files for loaddefs.el...20%
INFO Scraping files for loaddefs.el...30%
ERROR: Job failed: exit code 137
failed
test-filenotify-gio Test
  INFO     Scraping files for loaddefs.el...60% 
INFO Scraping files for loaddefs.el...70%
INFO Scraping files for loaddefs.el...80%
INFO Scraping files for loaddefs.el...90%
INFO Scraping files for loaddefs.el...100%
INFO Scraping files for loaddefs.el...done
make[3]: Leaving directory '/builds/emacs/emacs/lisp'
ELC ../lisp/abbrev.elc
ERROR: Job failed: exit code 137