compat: suppress deprecation warnings that are internal or during test.

nmigen/test/compat/support.py

@@ -1,10 +1,12 @@
+from ...tools import _ignore_deprecated
 from ...compat import *
 from ...compat.fhdl import verilog
 
 
 class SimCase:
     def setUp(self, *args, **kwargs):
-        self.tb = self.TestBench(*args, **kwargs)
+        with _ignore_deprecated():
+            self.tb = self.TestBench(*args, **kwargs)
 
     def test_to_verilog(self):
         verilog.convert(self.tb)