[llvm] r209007 - Fix most of PR10367.

[Rafael Espíndola]

> I’m sorry that I didn’t see your patch before you committed.  Can you explain
> what benefits this has over allowing a (restricted) ConstantExpr in the
> aliasee?
>
> My understanding is that Chris has changed his mind since he originally
> filed PR10367.  It certainly seems to me that, if we’re going to support
> non-zero offsets and addrspace conversions and so on in aliases, it’s
> far better to allow a restricted restricted set of constant expressions than
> it is to awkwardly replicate all of that functionality specifically for
> GlobalAlias.

The benefit is that ContantExpr is far more general than what is
needed. Simply allowing two different types covers all the uses that
were working on trunk. The missing feature is offsets.

I am actively working on getting offsets working. In fact I decided to
fix PR10367 first so I could get the three in a clean state before
adding support for offsets.

Cheers,
Rafael