Add fallback definitions of `DBL_EPSILPN` and `LDBL_EPSILON`; fix
This is a workaround for mingw-w64 (5.3.1) bug.
#include "mrbconf.h"
+#ifndef DBL_EPSILON
+#define DBL_EPSILON ((double)2.22044604925031308085e-16L)
+#endif
+#ifndef LDBL_EPSILON
+#define LDBL_EPSILON (1.08420217248550443401e-19L)
+#endif
+
#ifdef MRB_USE_FLOAT
#define MRB_FLOAT_EPSILON FLT_EPSILON
#else
