options/posix: Add endianness #defs in sys/param.h
#ifndef _SYS_PARAM_H
#define _SYS_PARAM_H
+#ifdef __GNUC__
+# define BYTE_ORDER __BYTE_ORDER__
+# define LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
+# define BIG_ENDIAN __ORDER_BIG_ENDIAN__
+# define PDP_ENDIAN __ORDER_PDP_ENDIAN__
+#else
+# error "Unsupported compiler"
+#endif
+
#ifdef __cplusplus
extern "C" {
#endif
