[clang] [clang] Don't use `VarDecl` of local variables as `ManglingContextDecl` for lambdas (PR #179035)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin commented:

@zygoloid @zyn0217 and @mizvekov might have opinions on this.

Should we not use the DC of the variable (ie its parent) ?
Did you cross check with gcc?

https://github.com/llvm/llvm-project/pull/179035