We were checking out the rustc repo multiple times on auto macOS, and
that was causing an error on the Azure side since multiple checkouts are
apparently not supported. This removes the extra checkout.
This commit is intended to go through and review/refactor the azure
pipelines configuration we have. The major changes are:
* The separate `{windows,macos,linux}.yml` files are now all merged into
one `run.yml`. This allows a shared "master flow" for all platforms
with divergence only where necessary.
* Some install steps have been separated as `install-*.yml` scripts,
where each script internally matches on the appropriate OS and then
delegates accordingly.
* Some various bits and pieces of cruft have been removed which were
artifacts of Travis's setup or similar.
As the infra team we decided to have an hard timeout of 3 hours on all
the jobs: while this sometimes causes spurious timeout errors it's a
great limit to prevent CI time to grow even more.
Pietro Albini
Alex Crichton
John Erickson