LibC: Implement getopt_long{,_only}

Few ports attempt to use this so lets add them :D

userspace/libraries/LibC/include/bits/getopt.h

@@ -0,0 +1,15 @@
+#ifndef _BITS_GETOPT_H
+#define _BITS_GETOPT_H 1
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+int getopt(int argc, char* const argv[], const char* optstring);
+
+extern char* optarg;
+extern int   opterr, optind, optopt;
+
+__END_DECLS
+
+#endif