The current setup uses different ways for different platforms, with
different workarounds, even using extra configuration items for Windows.
Now that there can't be a difference between the host per the build
system and the host per rust, we can get rid of those configuration
items, and use a more common infrastructure.
We cannot, however, avoid using wrapper scripts, because per-target rust
link-arg flags don't work up great.
The downside is that multiplies the number of wrappers, as we now have
to have a different one for host and target, and then we have .bat files
and shell scripts for, respectively, Windows hosts, and other hosts.
Depends on D24321
Differential Revision: https://phabricator.services.mozilla.com/D24322
--HG--
extra : moz-landing-system : lando
