ltmain.in: Fix infinite loop for error messages

ltmain.in: Fix infinite loop for error messages

If an invalid argument is passed to options '--mode' or '--reorder-cache'
after a valid command, error messages will print infinitely:

  $ libtool --help --mode=MODE
  libtool:   error: invalid argument 'MODE' for --mode
  libtool:   error: invalid argument 'MODE' for --mode
  libtool:   error: invalid argument 'MODE' for --mode
  ...

* build-aux/ltmain.in: Remove 'break' in case statement to fix infinite
  loop, and add shift for option '--reorder-cache' to allow more options
  to be processed.