[clang] [Clang] Fix Itanium mangling crash for local lambda in ctor/dtor (PR #181068)

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eiytoq wrote:

@efriedma-quic 

> The test coverage here seems deficient: nothing is actually checking that the mangling that was causing the crash.

Could you clarify what exact mangling you think the test should check?

> Also, for the names that are covered, the mangling seems to be inconsistent with gcc.

The GCC mismatch looks pre-existing, so I think it should be handled separately.

https://github.com/llvm/llvm-project/pull/181068