mark foreach mingw expected failure

[SVN r30742]

status/explicit-failures-markup.xml

@@ -874,6 +874,7 @@
             <toolset name="vacpp"/>
             <toolset name="cw-8_3"/>
             <toolset name="sunpro*"/>
+            <toolset name="mingw"/>
             <note author="Eric Niebler">
                 This compiler does not support detection of
                 const rvalues.