Colorize %L and %C text to match diagnostic_show_locus (PR fortran/91426)

Colorize %L and %C text to match diagnostic_show_locus (PR fortran/91426)

gcc/fortran/ChangeLog:
	PR fortran/91426
	* error.c (curr_diagnostic): New static variable.
	(gfc_report_diagnostic): New static function.
	(gfc_warning): Replace call to diagnostic_report_diagnostic with
	call to gfc_report_diagnostic.
	(gfc_format_decoder): Colorize the text of %L and %C to match the
	colorization used by diagnostic_show_locus.
	(gfc_warning_now_at): Replace call to diagnostic_report_diagnostic with
	call to gfc_report_diagnostic.
	(gfc_warning_now): Likewise.
	(gfc_warning_internal): Likewise.
	(gfc_error_now): Likewise.
	(gfc_fatal_error): Likewise.
	(gfc_error_opt): Likewise.
	(gfc_internal_error): Likewise.

From-SVN: r276132