Test T12504 on Windows

Test hsc2hs/T12504 is failing thus on Windows. Something path-y. Simon -{-# LINE 1 "T12504/path/to/T12504.hsc" #-} -{-# LINE 2 "T12504/path/to/T12504.hsc" #-} +{-# LINE 1 "T12504\\path\\to\\T12504.hsc" #-} +{-# LINE 2 "T12504\\path\\to\\T12504.hsc" #-} *** unexpected failure for T12504(normal)