libc: tag missing functions in system headers.

This matches recent changes in the NDK header.
We enclose missing functions in #if 0 .. #endif blocks
with a clear "MISSING" in comments in order to locate
them later.

Change-Id: I87b3a62e777897e75c9243360fb0a82bcc53d9fb
diff --git a/libc/include/getopt.h b/libc/include/getopt.h
index 6b4954b..56f1983 100644
--- a/libc/include/getopt.h
+++ b/libc/include/getopt.h
@@ -71,14 +71,19 @@
 #ifndef _GETOPT_DEFINED_
 #define _GETOPT_DEFINED_
 int	 getopt(int, char * const *, const char *);
-int	 getsubopt(char **, char * const *, char **);
+
 
 extern   char *optarg;                  /* getopt(3) external variables */
 extern   int opterr;
 extern   int optind;
 extern   int optopt;
 extern   int optreset;
+
+#if 0 /* MISSING FROM BIONIC */
+int       getsubopt(char **, char * const *, char **);
 extern   char *suboptarg;               /* getsubopt(3) external variable */
+#endif /* MISSING */
+
 #endif
 __END_DECLS