Handles the EINVAL and EFAULT cases in rt_sigprocmask. Some code uses this syscall to check whether a given address is valid; e.g. https://github.com/abseil/abseil-cpp/blob/master/absl/debugging/internal/address_is_readable.cc#L85 This requires DR to return EFAULT as expected by the app.
Also adds tests for some error and success cases of rt_sigprocmask.
Fixes: #5254