PR 87488: Add --with-diagnostics-urls configuration option

PR 87488: Add --with-diagnostics-urls configuration option

2020-02-15  David Malcolm  <dmalcolm@redhat.com>
	    Bernd Edlinger  <bernd.edlinger@hotmail.de>

	PR 87488
	PR other/93168
	* config.in (DIAGNOSTICS_URLS_DEFAULT): New define.
	* configure.ac (--with-diagnostics-urls): New configuration
	option, based on --with-diagnostics-color.
	(DIAGNOSTICS_URLS_DEFAULT): New define.
	* config.h: Regenerate.
	* configure: Regenerate.
	* diagnostic.c (diagnostic_urls_init): Handle -1 for
	DIAGNOSTICS_URLS_DEFAULT from configure-time
	--with-diagnostics-urls=auto-if-env by querying for a GCC_URLS
	and TERM_URLS environment variable.
	* diagnostic-url.h (diagnostic_url_format): New enum type.
	(diagnostic_urls_enabled_p): rename to...
	(determine_url_format): ... this, and change return type.
	* diagnostic-color.c (parse_env_vars_for_urls): New helper function.
	(auto_enable_urls): Disable URLs on xfce4-terminal, gnome-terminal,
	the linux console, and mingw.
	(diagnostic_urls_enabled_p): rename to...
	(determine_url_format): ... this, and adjust.
	* pretty-print.h (pretty_printer::show_urls): rename to...
	(pretty_printer::url_format): ... this, and change to enum.
	* pretty-print.c (pretty_printer::pretty_printer,
	pp_begin_url, pp_end_url, test_urls): Adjust.
	* doc/install.texi (--with-diagnostics-urls): Document the new
	configuration option.
	(--with-diagnostics-color): Document the existing interaction
	with GCC_COLORS better.
	* doc/invoke.texi (-fdiagnostics-urls): Add GCC_URLS and TERM_URLS
	vindex reference.  Update description of defaults based on the above.
	(-fdiagnostics-color): Update description of how -fdiagnostics-color
	interacts with GCC_COLORS.