mark MPL unusable with SunPro 5.3

[SVN r30017]

status/explicit-failures-markup.xml

@@ -1103,6 +1103,14 @@
     <!-- MPL -->
     <library name="mpl">
 
+        <mark-unusable>
+            <toolset name="sunpro-5_3-sunos"/>
+            <note author="Aleksey Gurtovoy" date="10 Jul 2005">
+                The compiler is not supported by the library due to an
+                utterly broken templates support.
+            </note>
+        </mark-unusable>
+
         <mark-expected-failures>
             <test name="as_sequence"/>
             <test name="is_sequence"/>