Introduce DISTUTILS_USE_SDK as a flag to determine whether the
SDK environment should be used. Fixes #1508010.
diff --git a/Lib/distutils/msvccompiler.py b/Lib/distutils/msvccompiler.py
index d24d0ac..d725905 100644
--- a/Lib/distutils/msvccompiler.py
+++ b/Lib/distutils/msvccompiler.py
@@ -237,7 +237,7 @@
 
     def initialize(self):
         self.__paths = []
-        if os.environ.has_key("MSSdk") and self.find_exe("cl.exe"):
+        if os.environ.has_key("DISTUTILS_USE_SDK") and os.environ.has_key("MSSdk") and self.find_exe("cl.exe"):
             # Assume that the SDK set up everything alright; don't try to be
             # smarter
             self.cc = "cl.exe"