Replace reprinting decision logic

Replace reprinting decision logic

After this change, we no longer need to decide when we need
to set TCB_REPRINT, and when we don't: it's never needed :)

Well, almost. That pesky pid-changing execve needs special treatment.
If not it, it'd be possible to nuke TCB_REPRINT...

While at it, fix a case of mishandled -C.

* strace.c (printleader): Do not set TCB_REPRINT.
(trace): Set TCB_REPRINT only for execve with changing pid.
Fix mishandling of -C.
* syscall.c (trace_syscall_entering): Do not clear TCB_REPRINT.
(trace_syscall_exiting): Replace reprinting decision logic.
Remove call to printargs(): it is known to just return 0 here.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>