[PATCH] Microsoft mangling of return type deducing functions/lambdas that return local types

[David Majnemer]

  Ugh, the MS ABI is not very amenable to this sort of thing.  Current versions of MSVC cannot reason about the following source let alone mangle it:

    template <typename T>
    auto fun(T) {
      auto L = []() {
        struct M {};
        return M{};
      };
      return L();
    }
    auto doit() { return fun(0); }

  Heck, even GCC does strange things here:
  `_ZZ3funIiEDaT_ENUlvE_4_FUNEv` which demangles as `auto fun<int>(int)::'lambda'()::_FUN()`

  I'd prefer if we mangled L's type as: `'R<lambda'_{mangling_number}>::operator()() const::M`

http://llvm-reviews.chandlerc.com/D3221