Update explicit-failures-markup.xml

[skip ci]

status/explicit-failures-markup.xml

@@ -914,9 +914,9 @@
         <mark-expected-failures>
             <test name="invariant-ifdef"/>
             <test name="specify-nothing"/>
-            <toolset name="clang-gnu-linux-3.6"/>
-            <toolset name="clang-gnu-linux-3.7"/>
-            <toolset name="clang-gnu-linux-3.8"/>
+            <toolset name="clang-linux-3.6"/>
+            <toolset name="clang-linux-3.7"/>
+            <toolset name="clang-linux-3.8"/>
             <note author="Lorenzo Caminiti">
                 This test fails on this compiler because of a bug in its STL
                 implementation (undefined references to