win msvs: make express editions not use x64-x64 compiler

pylib/gyp/MSVSVersion.py

Index: pylib/gyp/MSVSVersion.py
diff --git a/pylib/gyp/MSVSVersion.py b/pylib/gyp/MSVSVersion.py
index bb30a7ba048938e2bd1ff86bceed2cd3f19a4c33..03b6d8ad42cc7f81b9aaa56c86829a18307264ad 100644
--- a/pylib/gyp/MSVSVersion.py
+++ b/pylib/gyp/MSVSVersion.py
@@ -96,9 +96,11 @@ class VisualStudioVersion(object):
       else:
         assert target_arch == 'x64'
         arg = 'x86_amd64'
-        if (os.environ.get('PROCESSOR_ARCHITECTURE') == 'AMD64' or
+        # Use the 64-on-64 compiler if we're not using an express
+        # edition and we're running on a 64bit OS.
+        if self.short_name[-1] != 'e' and (
+            os.environ.get('PROCESSOR_ARCHITECTURE') == 'AMD64' or
             os.environ.get('PROCESSOR_ARCHITEW6432') == 'AMD64'):
-          # Use the 64-on-64 compiler if we can.
           arg = 'amd64'
         return [os.path.normpath(
             os.path.join(self.path, 'VC/vcvarsall.bat')), arg]