brings in moby/buildkit#911 [docker-18.09] llbsolver: fix selectors dedupe (backport of https://github.com/moby/buildkit/pull/858) fixes https://github.com/moby/moby/issues/38964 Signed-off-by: Sebastiaan van Stijn <github@gone.nl> Upstream-commit: 083da4862d9c88b3b40d6f4e1b21f6ce76920fd6 Component: engine