Testsuite: only add -fno-warn-missed-specialisations for ghc>=7.11

It should be possible to run the testsuite with older versions of GHC.

Reviewed by: austin

Differential Revision: https://phabricator.haskell.org/D1308

testsuite/mk/ghc-config.hs

@@ -34,6 +34,12 @@ main = do
         _ -> "package-conf"
   putStrLn $ "GhcPackageDbFlag" ++ '=':pkgdb_flag
 
+  let minGhcVersion711 = case lookup "Project version" fields of
+        Just v
+          | parseVersion v >= [7,11] -> "YES"
+        _ -> "NO"
+  putStrLn $ "MinGhcVersion711" ++ '=':minGhcVersion711
+
 
 getGhcFieldOrFail :: [(String,String)] -> String -> String -> IO ()
 getGhcFieldOrFail fields mkvar key

testsuite/mk/test.mk

@@ -44,9 +44,11 @@ TEST_HC_OPTS = -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-
 #
 TEST_HC_OPTS += -fno-warn-tabs
 
+ifeq "$(MinGhcVersion711)" "YES"
 # Don't warn about missing specialisations. They can only occur with `-O`, but
 # we want tests to produce the same output for all test ways.
 TEST_HC_OPTS += -fno-warn-missed-specialisations
+endif
 
 RUNTEST_OPTS =