Full error messages:

MSVC15:

2>c:\(...)\classes\helpertypes.h(87): error C2679: binary '<<': no operator found which takes a right-hand operand of type 'const mx::Point' (or there is no acceptable conversion)
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(495): note: could be 'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_streambuf<char,std::char_traits<char>> *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(475): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(const void *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(455): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long double)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(435): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(double)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(415): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(float)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(395): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned __int64)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(375): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(__int64)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(355): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned long)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(335): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(315): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned int)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(290): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(int)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(270): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned short)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(236): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(short)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(216): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(bool)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(209): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::ios_base &(__cdecl *)(std::ios_base &))'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(202): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ios<char,std::char_traits<char>> &(__cdecl *)(std::basic_ios<char,std::char_traits<char>> &))'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(196): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ostream<char,std::char_traits<char>> &(__cdecl *)(std::basic_ostream<char,std::char_traits<char>> &))'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(692): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(739): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(777): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(824): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(950): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const signed char *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(957): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,signed char)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(964): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const unsigned char *)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(971): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,unsigned char)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(981): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>,mx::Point>(std::basic_ostream<char,std::char_traits<char>> &&,const _Ty &)'
2>          with
2>          [
2>              _Ty=mx::Point
2>          ]
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(1019): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const std::error_code &)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\random(2568): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const std::bernoulli_distribution &)'
2>  c:\program files (x86)\microsoft visual studio 14.0\vc\include\thread(246): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,std::thread::id)'
2>  c:\(...)\classes\helpertypes.h(87): note: while trying to match the argument list '(std::ostringstream, const mx::Point)'
2>  c:\(...)\classes\(...)\entity\tinyent\tinyent.cpp(1502): note: see reference to function template instantiation 'std::string mx::to_string<mx::Point>(const T &)' being compiled
2>          with
2>          [
2>              T=mx::Point
2>          ]



MinGW 4.7.3:

In file included from jni/../../Classes/utilities/pattern/pat.h:5:0,
                 from jni/../../Classes/(...)/entity/tinyent/../ent.h:3,
                 from jni/../../Classes/(...)/entity/tinyent/tinyent.h:2,
                 from jni/../../Classes/(...)/entity/tinyent/tinyent.cpp:1:
jni/../../Classes/helpertypes.h: In instantiation of 'std::string mx::to_string(const T&) [with T = mx::Point; std::string = std::basic_string<char>]':
jni/../../Classes/(...)/entity/tinyent/tinyent.cpp:1502:20:   required from here
jni/../../Classes/helpertypes.h:87:5: error: cannot bind 'std::basic_ostream<char>' lvalue to 'std::basic_ostream<char>&&'
  os << val;
     ^
In file included from jni/../../Classes/utilities/pattern/abspat.h:6:0,
                 from jni/../../Classes/utilities/pattern/pat.h:3,
                 from jni/../../Classes/(...)/entity/tinyent/../ent.h:3,
                 from jni/../../Classes/(...)/entity/tinyent/tinyent.h:2,
                 from jni/../../Classes/(...)/entity/tinyent/tinyent.cpp:1:
C:/Users/(...)/Documents/libs/android-ndk-r10e/sources/cxx-stl/gnu-libstdc++/4.9/include/ostream:602:5: note: initializing argument 1 of 'std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Tp = mx::Point]'
     operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
     ^