[dfsan] Set sigemptyset's return label to be 0

[stephan.yichao.zhao]

Summary

This was not set from when the wrapper was introduced.

compiler-rt/lib/dfsan/dfsan_custom.cpp

return __dfsw_sched_getaffinity(pid, cpusetsize, mask, pid_label,
                                   cpusetsize_label, mask_label, ret_label);
 }
 
 SANITIZER_INTERFACE_ATTRIBUTE
 int __dfsw_sigemptyset(sigset_t *set, dfsan_label set_label,
                        dfsan_label *ret_label) {
   int ret = sigemptyset(set);
   dfsan_set_label(0, set, sizeof(sigset_t));
+  *ret_label = 0;
   return ret;
 }
 
 SANITIZER_INTERFACE_ATTRIBUTE
 int __dfso_sigemptyset(sigset_t *set, dfsan_label set_label,
                        dfsan_label *ret_label, dfsan_origin set_origin,
                        dfsan_origin *ret_origin) {
   return __dfsw_sigemptyset(set, set_label, ret_label);