Increase fiber stack size if UBSAN is enabled
Increase fiber stack size if UBSAN is enabled

Summary: UBSAN instrumentation results in more stack being used. Applying the same logic we already have for ASAN there.

Reviewed By: igorsugak

Differential Revision: D4287455

fbshipit-source-id: 1a224cb5a3654c23b15fa298bf80476234a1418c

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