Redefinitions of constexpr static data members are allowed now? (but not inline const)?

The following fails to compile under both gcc and clang in c++14, but succeeds with c++1z:

struct Cls {
  static constexpr int N = 0;
};
constexpr int Cls::N;
constexpr int Cls::N;

The C++14 error is predictable: redefinition of ‘constexpr const int Cls::N’

What changed to make this legal? I found:

n4659 10.1.5 [dcl.constexpr]

A function or static data member declared with the constexpr specifier is implicitly an inline function or variable

So I thought it might have to do with inline variables, but the following fails for c++1z under both compilers

struct Cls {
  static inline const int N = 0;
};
inline const int Cls::N; // note, only one definition here