fix Issue 12121 - atomicLoad!(MemoryOrder.acq) doesn't require load barrier

[Issue 12121 – atomicLoad!(MemoryOrder.acq) should not emit additional code on X86](https://d.puremagic.com/issues/show_bug.cgi?id=12121)
Merge pull request #723 from MartinNowak/fix12121

fix Issue 12121 - atomicLoad!(MemoryOrder.acq) doesn't require load barrier