Unbreak unittest-buck

[swolchok]

Fixed a couple clear OSS build problems, but ran into blockers (supported_features doesn't work in OSS buck), so just dropping prim_ops_test_cpp from OSS unittest-buck.

[swolchok]

Stack from ghstack (oldest at bottom):

• Include custom_ops and XNNPACK in executor_runner if built #9248
• -> Unbreak unittest-buck #9315

[pytorch-bot]

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[swolchok]

seeing torchgen_files error on unittest-buck for mac; IIRC this is flaking (no idea how but I bet it's the runner only having these files sometimes) and so I'm landing anyway once unittest-buck for linux passes since this is a clear step forward