V4 IR: fix type inference.

V4 IR: fix type inference.

When a phi-node couldn't be fully typed (e.g., when one of the temps
was not yet typed), VarType was assumed. When a circular dependency
between two phi-nodes occurred, like with a condition inside a loop,
then depending on the ordering of the work-list, the two phi-nodes
could start oscillating between VarType and the correct type.

The fix is to check if one of the temps is not fully typed, and if so,
assume whatever we currently have as the result and have the statement
re-scheduled. Full typing will occur when the temp with the missing
type information is typed.

Change-Id: I950d81fe7fa8272cb37f7eea5b88092d1eb4817e
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>