[clang] [Clang] Emit error for duplicate mangled names within a lambda (PR #107581)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

> The SME type attributes are not part of the name mangling

If `int(&)() __arm_streaming` is a different type from `int(&)()` for template instantiation, it should have different mangling.  If it doesn't, that's a bug.  If there is no spec for the correct mangling, someone should write a spec.

https://github.com/llvm/llvm-project/pull/107581