[clang] [clang][Parser] Allow private type aliases in out-of-line member function return types (PR #169272)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

> @vgvassilev Would you mind please reviewing this for viability? It's a very small change, but I can't be sure it's the correct way to go about this. We're aiming to solve this problem #164885 which currently prevents `clang::Interpreter` from using boost.asio.

This is not the way to go. We should fix this issue in the tentative parsing logic around: https://github.com/llvm/llvm-project/blob/e04c01bcc91226d632f81bd3290c180deb0b6db8/clang/lib/Parse/ParseTentative.cpp#L56-L63


https://github.com/llvm/llvm-project/pull/169272