test.support: Add dummy @requires_IEEE_754 decorator.

Used e.g. by datetime/test_datetime.py.

test.support/test/support.py

@@ -60,3 +60,6 @@ def captured_output(stream_name):
 
 def captured_stderr():
     return captured_output("stderr")
+
+def requires_IEEE_754(f):
+    return f