Before this commit, many passes in revng-c were skipping over
non-isolated functions.
Now revng-pipeline takes care of removing non-isolated functions so that
check can be omitted everywhere.
This commits changes the ExitSSAPass to ensure that StoreInst are placed
ASAP, close to the computation of the incoming Values of the replaced
PHINode.
This generates IR that typically yields less local variables in
SwitchToStatements.
Alessandro Di Federico