* cpperror.c (cpp_file_line_for_message): If 'line' is zero,
	just print "<command line>".  If 'filename' is null or an
	empty string, print "<stdin>" for the filename.
	* cpplib.c (do_define): Don't print the 'location of the
	previous definition' message if we're still parsing the
	command line.
	(cpp_pedwarn_with_file_and_line): Always call
	cpp_file_line_for_message.

From-SVN: r31697