[clang] [clang][ItaniumMangle] Fix mangling of lambdas in default member initializers of local classes (PR #206740)

[Kristina Bessonova via cfe-commits]

chbessonova wrote:

> Perhaps? Every time I personally determine "we probably don't need one because there is no WAY this can escape the TU!" I've been wrong :D

Fair enough 😄. I added the compatibility entry.

https://github.com/llvm/llvm-project/pull/206740