ZC: fix issue #55.

GAS tries to relax a conditional branch by flipping the condition bit
and setting the offset to a two-instruction-length constant.

relax
    bne	t5,t3,.Lfar_away
to
    beq	t5,t3,8 # a constant value
    j .Lfar_away

To solve this issue, we add a local symbol right after the `j`
instruction, and then the linker can help adjust bytes during
linker relaxation.