bswap/W64 test fails on i386

      W64:                FAIL (7.80s)
        *** Failed! Falsified (after 51 tests and 2 shrinks):
        -(zext[W16→W64](load[W16](0xc::W32)))
        test ( bits32 buffer ) {
          bits64 ret;
          (ret) = prim %bswap64(%neg(%zx64(bits16[buffer + (12 :: bits32)])));
          return (ret);
        }
        
        0xfcfaffffffffffff /= 0xfcfafffffcfaffff
        Use --quickcheck-replay="(SMGen 11301759829851052901 7931391100024291857,50)" to reproduce.
        Use -p '$2!~/llvm/&&/bswap.W64/' to rerun this test only.