Fix markup for sun-5.8

[SVN r35680]

status/explicit-failures-markup.xml

@@ -1926,7 +1926,7 @@
         </mark-expected-failures>
        <mark-expected-failures>
           <test name="vector_c"/>
-          <toolset name="sun-5_8"/>
+          <toolset name="sun-5.8"/>
           <note author="John Maddock">
              This is reported to be fixed in the next Sun
              compiler release.