Add some 6.10-specific test outputs

testsuite/tests/ghc-regress/gadt/gadt-escape1.stderr-6.10

+
+gadt-escape1.hs:16:52:
+    GADT pattern match with non-rigid result type `t'
+      Solution: add a type signature
+    In a case alternative: Hidden (ExpInt _) a -> a
+    In the expression:
+        case (hval :: Hidden) of { Hidden (ExpInt _) a -> a }
+    In the definition of `weird1':
+        weird1 = case (hval :: Hidden) of { Hidden (ExpInt _) a -> a }

testsuite/tests/ghc-regress/gadt/gadt13.stderr-6.10

+
+gadt13.hs:12:5:
+    GADT pattern match in non-rigid context for `I'
+      Solution: add a type signature
+    In the pattern: I t
+    In the definition of `shw': shw (I t) = ("I " ++) . shows t

testsuite/tests/ghc-regress/gadt/gadt7.stderr-6.10

+
+gadt7.hs:12:31:
+    GADT pattern match in non-rigid context for `K'
+      Solution: add a type signature
+    In the pattern: K
+    In a case alternative: K -> y1
+    In the expression: case t1 of { K -> y1 }
+
+gadt7.hs:15:32:
+    GADT pattern match in non-rigid context for `K'
+      Solution: add a type signature
+    In the pattern: K
+    In a case alternative: K -> y1
+    In the expression: case t1 of { K -> y1 }

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail172.stderr-6.10

+
+tcfail172.hs:19:10:
+    GADT pattern match in non-rigid context for `Nil'
+      Solution: add a type signature
+    In the pattern: Nil
+    In the definition of `is_normal': is_normal Nil = True