[clang] [clang][Sema] Handle target_clones redeclarations that omit the attribute (PR #169259)

[Henry Baba-Weiss via cfe-commits]

henrybw wrote:

> I think this is right. I'm happy to let this go and see what happens.

@erichkeane Thanks for the review! I don't have commit access, so could you merge this on my behalf?

https://github.com/llvm/llvm-project/pull/169259