testsuite: Mark test for #12355 as unbroken on Darwin.
testsuite: Mark test for #12355 as unbroken on Darwin.

Somehow this testcase works on Darwin but not on Linux. This deserves
further investigation.

shlevy/ghc,sdiehl/ghc,snoyberg/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,olsner/ghc,mettekou/ghc,olsner/ghc,ezyang/ghc,sdiehl/ghc,olsner/ghc,shlevy/ghc,sdiehl/ghc,snoyberg/ghc,olsner/ghc,shlevy/ghc,snoyberg/ghc,shlevy/ghc,ezyang/ghc,mettekou/ghc,snoyberg/ghc,sdiehl/ghc,mettekou/ghc,olsner/ghc,mettekou/ghc,mettekou/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,olsner/ghc,snoyberg/ghc,sdiehl/ghc,snoyberg/ghc,mettekou/ghc,ezyang/ghc,sdiehl/ghc,olsner/ghc,ezyang/ghc,snoyberg/ghc,mettekou/ghc,ezyang/ghc