[clang] [clang] Allow overriding any global variable address space (PR #195612)

[Pierre van Houtryve via cfe-commits]

Pierre-vh wrote:

> I don't think this is [NFC] because it's introducing new functionality that can be used; I'd prefer to drop that from the summary and add test coverage showing that the override actually happens.

I removed the NFC tag, the is introduced in the next patch in the stack where we make use of that override. 
To test this in this patch I'd need a unit test I think, I can add some if you'd like - I just don't see any other test of this type for this API so I am not sure it is the preferred way.

https://github.com/llvm/llvm-project/pull/195612