[clang] [clang-tools-extra] [Clang] Use TargetInfo when deciding is an address space is compatible (PR #115777)

[John McCall via cfe-commits]

rjmccall wrote:

Oh, you can just forward-declare `class ASTContext` at the top of that file.  It's funny that that isn't already there.  

https://github.com/llvm/llvm-project/pull/115777