Partial revert of commit cf23e34187. This
mostly moved existing arguments to the "right" location, but also
introduced new arguments that didn't previously exist -- which was
wrong.
... also, these cross files are used by CI (if they have a corresponding
.json file) and this change broke the CI. Because --target isn't a valid
gcc option, although clang/rustc do accept it. For GCC, the argument
parser decides you wanted --target-help, which prints documentation text
and then quits.
6bfe5d3235