testblockalloc: run the threaded way with -I0, so it doesn't try to GC

testsuite/tests/ghc-regress/rts/all.T

-test('testblockalloc', compose(c_src,
-                               only_ways(['normal','threaded1'])), 
+test('testblockalloc', compose(c_src, only_ways(['normal'])), 
+                       compile_and_run, [''])
+
+test('testblockalloc', compose(c_src, 
+                       compose(only_ways(['threaded1']),
+                               extra_run_opts('+RTS -I0'))), 
                        compile_and_run, [''])