add empty runner
add empty runner

this is required for compile-time experiments that only build when
they're actually executed. This will produce a lot of additional entries
in the database.


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Former-commit-id: 6a168a840041911a28f33847a14ce39b11d2d5ab [formerly 028250f6022adc8e452354dfa751cf408c1615f5]
Former-commit-id: c7b89fc39373907b3a375fdbb55203a659102c40
PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild