Fix develop error in getopt_long_only

The error was due to casting `const` away for permuting argv
elements, which is necessary for a libc for compatibility with older
systems, but not for us.

Checkpatch will complain about the style not being followed, but this is not
our code, so it can be ignored.

include/extern/getopt.h

@@ -36,7 +36,7 @@ struct option {
 	int val;
 };
 
-int getopt_long_only(int, char *const *, const char *, const struct option *, int *);
+int getopt_long_only(int, char **, const char *, const struct option *, int *);
 
 #define no_argument        0
 #define required_argument  1