[lld] r301438 - LTO: Mark undefined module asm symbols as used.

[Rafael Espíndola via llvm-commits]

> This is a small code quality regression. Before we had an internal GV
> that we knew we had to keep. Now we have an external GV.
>
> Would it be too hard to get it back?
>
> Cheers,
> Rafael
>
>
> Is there any difference between the two other than the linkage in the object
> file?

Now that I think of it, this can probably be counted as a bug fix.

The advantage of making something internal is that it can allow for
optimizations like a custom calling convention.

But these symbols are being used from assembly, so those optimizations
would be invalid.

Thanks,
Rafael