* src/getargs.c (short_options): Split and sort for readability.

* src/getargs.c (short_options): Split and sort for readability.
-g and -x take optional arguments, just like their long options.
* build-aux/cross-options.pl: Use /x to make the regexp easier to
understand.
Fix the handling of $opt which resulted in all the argument to be
considered as optional.