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

[Erich Keane via cfe-commits]

erichkeane wrote:

As I said before, the mechanism here of just creating a global-decl that promises a complete ctor/dtor is just wrong.  I'm still very much against this.  I don't have a great idea of what the right solution is, but this doesn't seem it to me.

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