getopt(): Update comments about missing functionality

Per the Linux man page, "By default, getopt() permutes the contents of argv as it scans, so that eventually all the nonoptions are at the end."  This behavior, however, is not implemented in the NuttX getopt() logic.

libs/libc/unistd/lib_getopt.c

@@ -65,6 +65,9 @@
  *      must call getopt() repeatedly and continue to parse if other
  *      errors are returned ('?' or ':') until getopt() finally returns -1.
  *      (You can also set optind to -1 to force a reset).
+ *   4. Standard getopt() permutes the contents of argv as it scans, so that
+ *      eventually all the nonoptions are at the end.  This implementation
+ *      does not do this.
  *
  * Returned Value:
  *   If an option was successfully found, then getopt() returns the option

libs/libc/unistd/lib_getopt_common.c

@@ -327,6 +327,9 @@ errout:
  *      must call getopt() repeatedly and continue to parse if other
  *      errors are returned ('?' or ':') until getopt() finally returns -1.
  *     (You can also set optind to -1 to force a reset).
+ *   4. Standard getopt() permutes the contents of argv as it scans, so that
+ *      eventually all the nonoptions are at the end.  This implementation
+ *      does not do this.
  *
  * Returned Value:
  *   If an option was successfully found, then getopt() returns the option