[Bug libstdc++/79384] New: Clang doesn't like variant's std::visit

[eric at efcs dot ca]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79384

            Bug ID: 79384
           Summary: Clang doesn't like variant's std::visit
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric at efcs dot ca
  Target Milestone: ---

The following example doesn't compile when using Clang to target libstdc++

Minimal reproducers:

// clang++ -std=c++1z test.cpp
#include <variant>
int main()
{
  std::visit([](auto&&) { }, std::variant<std::monostate>());
}

Example output:

https://godbolt.org/g/kSmBTg