When deciding where to split a block to insert stack guard checks, we should
move past any debug instructions we see that might (e.g.) be separating a tail
call from its frame wrangling.
This time, also don't run off the front of a basic block.
When deciding where to split a block to insert stack guard checks, we should
move past any debug instructions we see that might (e.g.) be separating a tail
call from its frame wrangling.
