[runtimes] Run backdeployment CI on Github hosted runners (#109984)
This removes the need for macOS nodes in Buildkite. It also moves to the
proper way of testing backdeployment, which is to actually run on the
target OS itself, instead of using packaged dylibs from previous OS
versions and trying to emulate backdeployment with DYLD_LIBRARY_PATH.
As a drive-by change, also fix a few back-deployment annotations that
were incorrect and add support for minor versions in the Lit feature
determining availability from the target triple.
NOKEYCHECK=True
GitOrigin-RevId: 0547e573c555445e37db5c3bc92ee72274e19b69
3 files changed
