Fix tests for new GHC (hide Prelude.<>)

Author: robx

Diff for: tests/Test.hs

@@ -11,6 +11,11 @@
 -- 3) Testing bug fixes (whitebox)
 --
 -----------------------------------------------------------------------------
+
+#if __GLASGOW_HASKELL__ >= 803
+import Prelude hiding ( (<>) )
+#endif
+
 import PrettyTestVersion
 import TestGenerators
 import TestStructures

Diff for: tests/TestStructures.hs

@@ -12,6 +12,10 @@ module TestStructures (
         text', annotToTd, tdToStr, genericCProp
     ) where
 
+#if __GLASGOW_HASKELL__ >= 803
+import Prelude hiding ( (<>) )
+#endif
+
 import PrettyTestVersion
 
 data CDoc = CEmpty           -- empty