system detection

#if defined(__linux__) || defined(__linux)
#  define MY_OS_LINUX
#endif

#ifdef MY_OS_LINUX
#    define MY_DECL_EXPORT     __attribute__((visibility("default")))
#    define MY_DECL_IMPORT     __attribute__((visibility("default")))
#    define MY_DECL_HIDDEN     __attribute__((visibility("hidden")))
#  else
#    define MY_DECL_EXPORT     __declspec(dllexport)
#    define MY_DECL_IMPORT     __declspec(dllimport)
#endif