cw-9_4-darwin is a required platform

[SVN r28632]

status/explicit-failures-markup.xml

@@ -20,6 +20,7 @@
     <mark-toolset name="cw-9_4" status="required"/>
     <mark-toolset name="cw-8_3" status="required"/>
     <mark-toolset name="cw-9_3-darwin" status="required"/>
+    <mark-toolset name="cw-9_4-darwin" status="required"/>
     <mark-toolset name="msvc" status="required"/>
     <mark-toolset name="msvc-stlport" status="required"/>
     <mark-toolset name="vc7" status="required"/>