Generated code now either jumps to `anypc` or `unexpectedpc`. The latter
one is to be considered a safety measure and will be populated with an
unreachable instruction on the decompilation pipeline.
This commit introduces the PruneRetSuccessors pass, whose role is to
identify all the indirect jumps whose devirtualized destinations
correspond to return addresses. In fact, they are most likely to be
return instructions and devirtualizing them is always detrimental.
Alessandro Di Federico