bcc enabled from string_algo builds

[SVN r28812]

status/explicit-failures-markup.xml

@@ -51,7 +51,6 @@
     <library name="algorithm/string">
         <mark-unusable>
             <toolset name="borland"/>
-            <toolset name="borland-5_6_4"/>
             <toolset name="msvc"/>
             <toolset name="msvc-stlport"/>
             <toolset name="iw-7_1-vc6"/>