Add riscv target, enhance arm target

src/fs.h

@@ -3,3 +3,10 @@
 #include "arch.h"
 
 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