hydra-eval-jobs: Reinitialize Boehm GC in the child

This is necessary to prevent hangs in the garbage collector.

Created by  Eelco Dolstra  on August 10, 2018
CXKN2W4BUREOIATFL5KYH7KMJWP2R3IG4V5GDQMOPPUKXUF2GOYAC
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