Some functions have their sizes as zero in input binary's symbol
table, like those compiled by assembler. When figuring out function
sizes, we may create label symbol if it doesn't point to any constant
island. However, before function size is known, marker symbol can
not be correctly associated to a function and therefore all such
checks would fail and we could end up adding a code label pointing
to constant island as secondary entry point and later mistakenly
marking the function as not simple.
Querying the global marker symbol array has big throughput overhead.
Instead we can run an extra check when post processing entry points
to identify such label symbols that actually point to constant islands.
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