constexpr static std::array

I have this code:

class ExternalGeometryExtension : public Part::GeometryExtension
{
public:
    enum Flag {
        Defining = 0,
        Frozen = 1, 
        Detached = 2,
        Missing = 3,
        Sync = 4,
        NumFlags
    };

    constexpr static std::array<const char *,NumFlags> flag2str Defining;
}

It compiles fine with: clang version 5.0.0 and gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4

It fails to compile with MSVC2013.

The compilation error is:

 C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C2143: syntax error : missing ';' before 'std::array<const char *,0x05>' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C2039: 'flag2str' : is not a member of 'Sketcher::ExternalGeometryExtension' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
         C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtensionPyImp.cpp(67): error C2039: 'flag2str' : is not a member of 'Sketcher::ExternalGeometryExtension' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]

Full compiler output here

My questions are: What I am doing wrong? Why is it not compiling with MSVC2013?

Is there something I can do to make this code work with MSVC2013 without breaking it in the other compilers?