testsuite: Enable T11627a on Darwin

The retainer profiler no longer uses the C stack for its mark stack (#14758).
Consequently even the small C stack provided on Darwin should be sufficient to
run this test. See #11627

testsuite/tests/profiling/should_run/all.T

@@ -115,10 +115,7 @@ test('T5363', [], compile_and_run, [''])
 
 test('profinline001', [], compile_and_run, [''])
 
-# Skip T11627a and T11627b on Darwin as it tends to give us a very small stack
-# which the retainer profiler tends to overflow. See #15287 and #11627.
 test('T11627a', [ extra_ways(extra_prof_ways)
-                , when(opsys('darwin'), skip)
                 ],
      compile_and_run, [''])