bpo-30342: Fix sysconfig.is_python_build() on VS9.0 (#1544)

Fix sysconfig.is_python_build() if Python is built with Visual Studio
2008 (VS 9.0).
diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index fa23220..2001c8e 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -267,6 +267,8 @@
             self.skipTest("Tools/buildbot/test.bat requires PCbuild build, "
                           "found %s" % build_dir)
 
+    @unittest.skipUnless(sysconfig.is_python_build(),
+                         'test.bat script is not installed')
     @unittest.skipUnless(sys.platform == 'win32', 'Windows only')
     def test_tools_buildbot_test(self):
         self.need_pcbuild()