Added incompatibility flag to prepare for flip in future Bazel versions

[abrisco]

A quick query seemed to prove the repo is compliant with incompatible_disallow_empty_glob but it'd be good to add regardless to avoid future regressions.

[QuantamHD]

/gcbrun

[QuantamHD]

/gcbrun

[QuantamHD]

Looks like there's some RPM related error https://app.buildbuddy.io/invocation/554468ea-d9a8-11ee-8ecb-0242c0a80a02

[abrisco]

Looks like there's some RPM related error https://app.buildbuddy.io/invocation/554468ea-d9a8-11ee-8ecb-0242c0a80a02

Yeah, I was definitely wrong when I mentioned the repo looked compliant. But the way the repo is tested is also slightly flawed. It shouldn't be checking @rules_pkg//... and things like that. Instead there should be sufficient uses of each external repo within rules_hdl to cover what needs to be tested. I think this might be blocked by bazelbuild/rules_pkg#825