Unbreak 'catch syscall' + multi-threading

[Doug Evans]

On Wed, Sep 30, 2009 at 5:48 PM, Pedro Alves <pedro@codesourcery.com> wrote:
> As we were discussing yesterday, 'catch syscall' is unfortunately
> broken with multi-threading in the mix, plus it has a few other
> problems (present on 7.0 too, of course).  This patch fixes all the
> issues I found.

Thanks.

> The code now uses (SIGTRAP | 0x80) directly in the couple
>   of places that need it, since that is exactly how the event is
>   described in the ptrace man page.

nit: 0x80 is still a magic  number no different than others (ISTM anyway).

IWBN to keep TRAP_IS_SYSCALL (change the name however you like &/|
only record 0x80 in it if you like).