[clang] [clang][FMV] Fix crash with cpu_specific attribute. (PR #115762)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

> Can you better explain what the crash cause is? It isn't clear what the change here is doing.

Oh sorry, I thought it became evident with the latest revision. The reason we are crashing is that we call takeName on the same Value. That is because when replaceDeclarationWith is called from the last callsite in the function, the arguments Resolver and ResolverGV are pointing to the same Value. We should be taking the early exist, that's why I am asserting that we aren't at the fallthrough with ResolverGV being non-null anymore. Does it make sense?

https://github.com/llvm/llvm-project/pull/115762