[BOLT] Fix handling of trailing entries in jump tables (#88444)

If a jump table has entries at the end that are a result of
__builtin_unreachable() targets, BOLT can confuse them with function
pointers. In such case, we should exclude these targets from the table
as we risk incorrectly updating the function pointers. It is safe to
exclude them as branching on such targets is considered an undefined
behavior.