5083 avoid undefined order of operations in assignments

*** 695,705 ****
           * Otherwise, if there are either no waiters, there may in fact be
           * pollers, so we do not signal in that case.
           */
          if (mblist->mbl_pollers > 0 && mblist->mbl_waiters > 0) {
                  /* flip the signal value */
!                 mblist->mbl_signal = (++mblist->mbl_signal) % 2;
          } else if (mblist->mbl_waiters > 0) {
                  mblist->mbl_signal = 1;
          } else {
                  mblist->mbl_signal = 0;
          }
--- 695,705 ----
           * Otherwise, if there are either no waiters, there may in fact be
           * pollers, so we do not signal in that case.
           */
          if (mblist->mbl_pollers > 0 && mblist->mbl_waiters > 0) {
                  /* flip the signal value */
!                 mblist->mbl_signal = (mblist->mbl_signal + 1) % 2;
          } else if (mblist->mbl_waiters > 0) {
                  mblist->mbl_signal = 1;
          } else {
                  mblist->mbl_signal = 0;
          }