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.
```
issue