Skip barton-mangler-bug(profc) in the 6.8 branch

It was hitting the timeout limit

testsuite/tests/ghc-regress/programs/barton-mangler-bug/test.T

 # Exhausts Hugs's heap (CAF leak)
 
 test('barton-mangler-bug',
-	compose(skip_if_fast, omit_compiler_types(['hugs'])),
+	composes([skip_if_fast,
+              omit_compiler_types(['hugs']),
+              if_compiler_lt('ghc', '6.9', omit_ways(['profc']))]),
 	multimod_compile_and_run, ['Main', ''])
 clean_o_hi()