Remove clang workaround.

Clang from llvm 2.8 doesn't need it. Clang form llvm 2.7 isn't
supported.

[SVN r66556]

libs/unordered

@@ -1 +1 @@
-Subproject commit a49c76c69c6e5adf53a089110965854d3e1c0a2d
+Subproject commit 2c1a8894cb8f09c6977380fa2d241bbece5cf243