target-arm: A64: Avoid duplicate exit_tb(0) in non-linked goto_tb
If gen_goto_tb() decides not to link the two TBs, then the
fallback path generates unnecessary code:
* if singlestep is enabled then we generate unreachable code
after the gen_exception_internal(EXCP_DEBUG)
* if singlestep is disabled then we will generate exit_tb(0)
twice, once in gen_goto_tb() and once coming out of the
main loop with is_jmp set to DISAS_JUMP
Correct these deficiencies by only emitting exit_tb() in the
non-singlestep case, in which case we can use DISAS_TB_JUMP
to suppress the main-loop exit_tb().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>