Fix for correct disassembling of conditional tail calls.

Summary:
BOLT attempts to convert jumps that serve as tail calls to dedicated tail call
instructions, but this is impossible when the jump is conditional because there is
no corresponding tail call instruction. This was causing the creation of a duplicate
fall-through edge for basic blocks terminated with a conditional jump serving as
a tail call when there is profile data available for the non-taken branch. In this
case, the first fall-through edge had a count taken from the profile data, while
the second has a count computed (incorrectly) by
BinaryFunction::inferFallThroughCounts.

(cherry picked from FBD3560504)