add 6.8 output

testsuite/tests/ghc-regress/deriving/should_fail/drvfail002.stderr-6.8

+
+drvfail002.hs:15:0:
+    Ambiguous constraint `X T c'
+        At least one of the forall'd type variables mentioned by the constraint
+        must be reachable from the type after the '=>'
+    In the instance declaration for `Show T'
+
+drvfail002.hs:18:0:
+    No instance for (X T c)
+      arising from the 'deriving' clause of a data type declaration
+                   at drvfail002.hs:18:0-25
+    Possible fix: add an instance declaration for (X T c)
+    When deriving the instance for (Show S)