Make range types inherit signed-ness from base type

Make range types inherit signed-ness from base type

I ran across this comment in valprint.c:

      /* FIXME: create_static_range_type does not set the unsigned bit in a
         range type (I think it probably should copy it from the target
         type), so we won't print values which are too large to
         fit in a signed integer correctly.  */

It seems to me that a range type ought to inherit its signed-ness from
the underlying type, so this patch implements this change, and removes
the comment.  (It was also copied into m2-valprint.c.)

I also remove the comment about handling ranges of enums, because I
think that comment is incorrect.

gdb/ChangeLog
2020-10-17  Tom Tromey  <tom@tromey.com>

	* valprint.c (generic_value_print): Remove comment.
	* m2-valprint.c (m2_value_print_inner): Remove comment.
	* gdbtypes.c (create_range_type): Set TYPE_UNSIGNED from base
	type.