Fixes backend/lower_call.c
Fixes backend/lower_call.c

- is_lowered_type is not helpful, because the flag may already be set
  by lower_calls before. This flag should probably be removed in general.
- hence lower_mtp must not check for is_lowered_type
- lower_Start must update the entity type, but not lower_irg,
  otherwise lower_Start can not decide, whether a lowering is necessary.

8l/libfirm,8l/libfirm,MatzeB/libfirm,killbug2004/libfirm,killbug2004/libfirm,jonashaag/libfirm,davidgiven/libfirm,MatzeB/libfirm,davidgiven/libfirm,MatzeB/libfirm,davidgiven/libfirm,jonashaag/libfirm,davidgiven/libfirm,8l/libfirm,8l/libfirm,killbug2004/libfirm,jonashaag/libfirm,jonashaag/libfirm,jonashaag/libfirm,killbug2004/libfirm,killbug2004/libfirm,killbug2004/libfirm,libfirm/libfirm,jonashaag/libfirm,killbug2004/libfirm,jonashaag/libfirm,libfirm/libfirm,8l/libfirm,davidgiven/libfirm,libfirm/libfirm,MatzeB/libfirm,davidgiven/libfirm,MatzeB/libfirm,8l/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,8l/libfirm,davidgiven/libfirm,MatzeB/libfirm