[llvm] r181328 - Mention SystemZ in the release notes

[Rafael Espíndola]

> It seems highly error-prone to try to merge these one by one. Maybe it would
> be better to just merge the whole document right before the release is made?
> That would avoid anything falling through the cracks. Or I guess it doesn't
> hurt to merge as we go, and then merge the whole document to make sure
> nothing got lost.

A related problem is where to put the 3.4 release notes. IMHO we
should merge what we have to 3.3 and start the 3.4 release notes. Any
new additions to the 3.3 release notes should then go directly to the
3.3 branch.

> -- Sean Silva
>

Cheers,
Rafael