add logging, use boost.log.

lichao

2021-05-06 0117d5f8ff386075b0c4cbec0cbe460fe3cfa680

 src/shm.h

@@ -68,7 +68,7 @@
         if (Killed(old)) {
            r = PidCas(old, pid());
            if (r) {
               printf("PidCheck captured pid %d -> %d\n", old, pid());
               LOG_DEBUG() << "PidCheck captured pid " << old << " -> " << pid();
            }
         }
      }