Define NDEBUG for releae builds, just like Python.

XXX Why doesn't distutils on Windows use the same set of flags as Python?

msvccompiler.py

@@ -233,7 +233,8 @@ class MSVCCompiler (CCompiler) :
             self.mc = "mc.exe"
 
         self.preprocess_options = None
-        self.compile_options = [ '/nologo', '/Ox', '/MD', '/W3', '/GX' ]
+        self.compile_options = [ '/nologo', '/Ox', '/MD', '/W3', '/GX' ,
+                                 '/DNDEBUG']
         self.compile_options_debug = ['/nologo', '/Od', '/MDd', '/W3', '/GX',
                                       '/Z7', '/D_DEBUG']