ifcvt: Fall through to NCE if getting the CE condition failed

ifcvt: Fall through to NCE if getting the CE condition failed

If getting the condition for conditional execution has failed then fall
through and try the non-conditional execution approach instead rather
than giving up with dead code elimination altogether, for a better code
structure if nothing else.

The case may well now be that whenever `cond_exec_get_condition' fails
`noce_get_condition' will as well, however in that case no change in
semantics will result.  If they ever diverge, then someone will have to
chase this place.

	gcc/
	* ifcvt.c (dead_or_predicable) [!IFCVT_MODIFY_TESTS]: Fall
	through to the non-conditional execution case if getting the
	condition for conditional execution has failed.