PR c/82050 reports a failed assertion deep within diagnostic_show_locus's
code for printing fix-it hints.

The root cause is a fix-it hint suggesting a textual replacement,
where the affected column numbers straddle the LINE_MAP_MAX_COLUMN_NUMBER
boundary, so that the start of the range has a column number, but the
end of the range doesn't.

The fix is to verify that the column numbers are sane when adding fix-it
hints to a rich_location, rejecting fix-it hints where they are not.

libcpp/ChangeLog:
	PR c/82050
	* include/line-map.h (LINE_MAP_MAX_COLUMN_NUMBER): Move here.
	* line-map.c (LINE_MAP_MAX_COLUMN_NUMBER): ...from here.
	(rich_location::maybe_add_fixit): Reject fix-it hints in which
	the start column exceeds the next column.

From-SVN: r255214