hadrian: Ignore warnings in unix and semaphore-compat

(cherry picked from commit dec81dd1)

hadrian/src/Flavour.hs

@@ -128,9 +128,13 @@ werror =
         ? notStage0
         ? mconcat
           [ arg "-Werror"
-          , flag CrossCompiling
-              ? package unix
+            -- unix has many unused imports
+          , package unix
               ? mconcat [arg "-Wwarn=unused-imports", arg "-Wwarn=unused-top-binds"]
+            -- semaphore-compat relies on sem_getvalue as provided by unix, which is
+            -- not implemented on Darwin and therefore throws a deprecation warning
+          , package semaphoreCompat
+              ? mconcat [arg "-Wwarn=deprecations"]
           ]
     , builder Ghc
         ? package rts