Fix warnings trivial warnings.

Fix warnings about:
 . Unused variables
 . format mismatch in printf/scanf format string and arguments
 . Missing parenthesis around assignment as truth values
 . Clang warnings anout unknown GCC pragma

lib/libpuffs/puffs.c

@@ -82,6 +82,7 @@ EXTERN char **env_argv;
 #define PUFFS_MAX_ARGS 20
 
 int __real_main(int argc, char* argv[]);
+int __wrap_main(int argc, char* argv[]);
 
 int __wrap_main(int argc, char *argv[])
 {