gh-138573: restrict testAtan2() the IEC 60559-compatible platforms

Section 7.12.4.4 of the C17 doesn't specify special values
for atan2() (and in particular permit domain error when
both arguments are zero).  The F.10.1.4 does.

Author: skirpichev

Lib/test/test_math.py

@@ -325,6 +325,8 @@ def testAtanh(self):
         self.assertRaises(ValueError, math.atanh, NINF)
         self.assertTrue(math.isnan(math.atanh(NAN)))
 
+    @unittest.skipIf(not sys.float_info.stdc_iec_559,
+                     "Support for the IEC 60559 floating-point standard expected.")
     def testAtan2(self):
         self.assertRaises(TypeError, math.atan2)
         self.ftest('atan2(-1, 0)', math.atan2(-1, 0), -math.pi/2)