Mark msvc as unsupported.

[SVN r28686]

status/explicit-failures-markup.xml

@@ -1499,6 +1499,13 @@ for more information.
             <note refid="2"/>
         </mark-unusable>
 
+        <mark-unusable>
+            <toolset name="msvc"/>
+            <toolset name="msvc-stlport"/>
+            <note refid="17"/>
+        </mark-unusable>
+
+
         <!-- Mark expected failures -->
 
         <test name="unicode_test*">