Fix race condition in PackageTests/NewBuild/CmdRun/Terminate

The "up and running" file was written before the signal handler
was installed, so it was possible for the test to kill the
subprocess before, leading to a missed "exiting" line in the
output.

I hope this fixes the sporadic failures we're seeing (haskell#8080).

Author: robx

cabal-testsuite/PackageTests/NewBuild/CmdRun/Terminate/Main.hs

@@ -4,13 +4,11 @@ import qualified System.Posix.Signals as Signal
 import System.Exit (exitFailure)
 
 main = do
-  writeFile "exe.run" "up and running"
   mainThreadId <- myThreadId
   Signal.installHandler Signal.sigTERM (Signal.Catch $ killThread mainThreadId) Nothing
-  sleep
-    `finally` putStrLn "exiting"
-  where
-    sleep = do
-      putStrLn "about to sleep"
-      threadDelay 10000000 -- 10s
-      putStrLn "done sleeping"
+  do
+    putStrLn "about to sleep"
+    writeFile "exe.run" "up and running"
+    threadDelay 10000000 -- 10s
+    putStrLn "done sleeping"
+  `finally` putStrLn "exiting"