[swig] fix wrong warning
%#if defined(__GNUC__)
%#pragma GCC diagnostic push
+%#ifdef __cplusplus
+%#pragma GCC diagnostic ignored "-Wmissing-declarations"
+%#else
%#pragma GCC diagnostic ignored "-Wmissing-prototypes"
%#endif
+%#endif
%#if NPY_API_VERSION < 0x00000007
%#define NPY_ARRAY_DEFAULT NPY_DEFAULT
