Recharacterize test according to discussion in #8851.

(cherry picked from commit 8ee6162e)

Conflicts:
	testsuite/tests/deriving/should_compile/all.T

testsuite/tests/deriving/should_compile/all.T

@@ -45,4 +45,3 @@ test('T8138', reqlib('primitive'), compile, ['-O2'])
 test('T8631', normal, compile, [''])
 test('T8758', extra_clean(['T8758a.o', 'T8758a.hi']), multimod_compile, ['T8758a', '-v0'])
 test('T8865', normal, compile, [''])
-test('T8851', expect_broken(8851), compile, [''])

testsuite/tests/deriving/should_fail/T8851.stderr

+
+T8851.hs:24:12:
+    Could not coerce from ‘Monad Parser’ to ‘Monad MyParser’
+      because the first type argument of ‘Monad’ has role Nominal,
+      but the arguments ‘Parser’ and ‘MyParser’ differ
+      arising from the coercion of the method ‘notFollowedBy’ from type
+                   ‘forall a. (Monad Parser, Show a) => Parser a -> Parser ()’ to type
+                   ‘forall a. (Monad MyParser, Show a) => MyParser a -> MyParser ()’
+    Possible fix:
+      use a standalone 'deriving instance' declaration,
+        so you can specify the instance context yourself
+    When deriving the instance for (Parsing MyParser)

testsuite/tests/deriving/should_fail/all.T

@@ -48,4 +48,5 @@ test('T7148', normal, compile_fail, [''])
 test('T7148a', normal, compile_fail, [''])
 test('T7800', normal, multimod_compile_fail, ['T7800',''])
 test('T5498', normal, compile_fail, [''])
-test('T6147', normal, compile_fail, [''])
\ No newline at end of file
+test('T6147', normal, compile_fail, [''])
+test('T8851', normal, compile_fail, [''])