linux-user: Trace rt_sigprocmask's sigsets

linux-user: Trace rt_sigprocmask's sigsets

Add a function for formatting target sigsets. It can be useful for
other syscalls in the future, so put it into the beginning of strace.c.
For simplicity, do not implement the strace's ~[] output syntax.

Add a rt_sigprocmask return handler.

Example outputs:

    753914 rt_sigprocmask(SIG_BLOCK,[SIGCHLD SIGTSTP SIGTTIN SIGTTOU],0x00007f80fddfe380,8) = 0 (oldset=[SIGTTOU])
    753914 rt_sigprocmask(SIG_SETMASK,[SIGCHLD],NULL,8) = 0
    753914 rt_sigprocmask(SIG_BLOCK,NULL,0x00007f80fddff3c0,8) = 0 (oldset=[])

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20241022102726.18520-1-iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>