Could not make this code cross compile between MSVC 2015 and GCC 7.3

This seems to work for all compilers I have tested:

template <typename X>
template <typename Y>
inline auto Outer<X>::Inner<Y>::operator++() 
    -> Inner<Y> &
{
    ++y;
    return *this;
}

VS 2017 (15.9 update) builds this code just fine. Upgrade to the latest version which is more C++11/C++14 compliant than VS 2015 Update 3.

cl /permissive- /W4 /EHsc t.cpp

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