Fix breakage caused by already-flipped flags (#898)
Fix breakage caused by already-flipped flags (#898)

Bazelisk may return already flipped flags if projects pin their Bazel version (e.g. 0.29.0 for Buildfarm).
This commit restores the legacy behavior of silently ignoring such flags.
However, in the future we should print a warning, and we should also remove INCOMPATIBLE_FLAGS and get all information from Bazelisk.

Part of #869
bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration