Silence g++ 4.9 build issue

lib/Support/ThreadLocal.cpp:53:15: error: typedef 'SIZE_TOO_BIG' locally defined but not used [-Werror=unused-local-typedefs]
   typedef int SIZE_TOO_BIG[sizeof(pthread_key_t) <= sizeof(data) ? 1 : -1];

Done the C++11 way, switching on and using LLVM_STATIC_ASSERT() instead of LLVM_ATTRIBUTE_UNUSED.
Silence g++ 4.9 build issue

lib/ASTMatchers/ASTMatchFinder.cpp:276:28: error: typedef 'traverse_can_only_be_instantiated_with_base_type' locally defined but not used [-Werror=unused-local-typedefs]
                            traverse_can_only_be_instantiated_with_base_type);