sigreturn: print signal mask as a syscall argument

Although sigreturn takes signal mask via frame pointer,
it's more convenient to display signal mask as a syscall argument
rather than an outstanding object of unknown nature:

Before this change:
    sigreturn() (mask [USR2 CHLD RT_2 RT_3 RT_4 RT_31 RT_32]) = 0

After this change:
    sigreturn({mask=[USR2 CHLD RT_2 RT_3 RT_4 RT_31 RT_32]}) = 0

* signal.c (sys_sigreturn): Display signal mask as a syscall argument.
1 file changed