Subzero: Make thread_local work under MacOS 10.6.

src/IceCfg.h

Index: src/IceCfg.h
diff --git a/src/IceCfg.h b/src/IceCfg.h
index 15f353cb56226d331eee5fd198d1fef1d601d399..b7b6cde47e6bb3dd491e5318866bf58472d0a840 100644
--- a/src/IceCfg.h
+++ b/src/IceCfg.h
@@ -213,7 +213,7 @@ private:
   // Maintain a pointer in TLS to the current Cfg being translated.
   // This is primarily for accessing its allocator statelessly, but
   // other uses are possible.
-  thread_local static const Cfg *CurrentCfg;
+  ATTRIBUTE_TLS static const Cfg *CurrentCfg;
 };
 
 } // end of namespace Ice