[BOLT] Fix support for PIC jump tables

Summary:
BOLT heuristics failed to work if false PIC jump table entries were
accepted when they were pointing inside a function, but not at
an instruction boundary.

This fix checks if the destination falls at instruction boundary, and
if it does not, it truncates the jump table. This, of course, still does not
guarantee that the entry corresponds to a real destination, and we can
have "false positive" entry(ies). However, it shouldn't affect
correctness of the function, but the CFG may have edges that are never
taken. We may update an incorrect jump table entry, corresponding to an
unrelated data, and for that reason we force moving of jump tables if a
PIC jump table was detected.

(cherry picked from FBD8559588)