[tkln]

Care to elaborate on how that's supposed work in practice?

[scatters]

Wow, ugly, but it works:

    (void) R"long-comment(
    /* C-style comment */
    std::cout << "hello" << std::endl;
    )long-comment";

[ksherlock]

Ugly, confusing, hard to undo, and only works within a function (since it's a statement).