T7170 fails on Windows
As of https://gitlab.haskell.org/ghc/ghc/-/jobs/97843.
--- ffi/should_run/T7170.run/T7170.stderr.normalised 2019-06-11 06:44:45.850716500 +0000
+++ ffi/should_run/T7170.run/T7170.run.stderr.normalised 2019-06-11 06:44:45.852670300 +0000
@@ -1 +0,0 @@
-T7170: thread blocked indefinitely in an MVar operation