Add riscv target, enhance arm target

mongoose.h

@@ -608,6 +608,13 @@ void mg_usleep(unsigned long usecs);
 
 FILE *mg_fopen_packed(const char *path, const char *mode);
 
+#if defined(__linux__) && defined(GCC)
+#define MG_ENABLE_PACKED_FS 1
+#define MG_FOPENCOOKIE
+#else
+#define MG_ENABLE_PACKED_FS 0
+#endif
+
 
 
 unsigned short mg_url_port(const char *url);