r203052 - Construct GlobalValues with the correct linkage instead of using setLinkage.

[Rafael Espíndola]

> This is changing the linkage. Can you add comment why changing this will not change visibility of the symbol.
> Also, please add a test for this change.

Sorry, I should have been more clear in the commit message. There is
no functionality change. We just set the linkage at construction time
instead of setting it afterwards with setLinkage.

Cheers,
Rafael