[clang] [Clang] Fix mangling for struct initializers and invalid lambdas (PR #232357)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

Have you compared the manglings against gcc?

Is the mangling derived from somewhere in the Itanium spec?  If not, is there an open bug at https://github.com/itanium-cxx-abi/cxx-abi/issues ?

Please submit one patch per subject; the lambda crash seems unrelated.

https://github.com/llvm/llvm-project/pull/232357