[patch] Don't allow alias to point to declarations

[Nick Lewycky]

Rafael Espíndola wrote:
> On 23 October 2013 15:00, Rafael Espíndola<rafael.espindola at gmail.com>  wrote:
>> Ping. The clang side has been fixed.
>
> Ping

Please bring up the IR change on llvm-dev. Yes I understand that no .o 
format we know of supported this, but it's entirely possible for someone 
to have used this IR feature in combination with llvm-link. (If this 
step turns out to not be a formality, I'll be surprised.)

The patch essentially LGTM except that we shouldn't be talking about the 
"object file level" in LangRef, we just state that aliases must refer to 
definitions and thus it is so. Clarifying whether an alias is guaranteed 
to have the same address as its aliasee would be nice (is it? or is it 
merely "it may"?).

Nick