Add test for the new magic treatment of 'seq' in RULES

tests/ghc-regress/simplCore/should_run/SeqRule.hs

+
+-- This test checks that the magic treatment of RULES 
+-- for 'seq' works right. 
+--
+-- See Note [RULES for seq] in MkId for more details
+
+module Main where
+
+{-# NOINLINE f #-}
+f x = not x
+
+{-# RULES 
+     "f/seq" forall n e.  seq (f n) e = True
+ #-}
+
+main = print (seq (f True) False)

tests/ghc-regress/simplCore/should_run/SeqRule.stdout

+True

tests/ghc-regress/simplCore/should_run/all.T

@@ -27,3 +27,5 @@ test('simplrun010', composes([extra_run_opts('24 16 8'),
 # the output of -ddump-rules can be compared
 test('T2486', normal, compile, [''])
 test('T2756', normal, compile_and_run, [''])
+
+test('SeqRule', only_ways(['optc','optasm']), compile_and_run, [''])