testsuite: Don't run T16525a with -DS unless compiler_debugged

Originally I was thinking of just skipping the test unless
compiled_debugged==True. However, the test will likely be useful even
without -DS, so let's run it either way.

testsuite/tests/ghci/T16525a/all.T

 test('T16525a',
      [extra_files(['A.hs', 'B.hs', ]),
-      extra_run_opts('+RTS -DS -RTS'),
+      when(compiler_debugged(), extra_run_opts('+RTS -DS -RTS')),
+      # We don't support unloading with the dynamic linker
       when(ghc_dynamic(), skip), ],
      ghci_script, ['T16525a.script'])