Added rudimentary C++0x attribute support.

The following attributes are currently supported in C++0x attribute
lists (and in GNU ones as well):
 - align() - semantics believed to be conformant to n3000, except for
   redeclarations and what entities it may apply to
 - final - semantics believed to be conformant to CWG issue 817's proposed
   wording, except for redeclarations
 - noreturn - semantics believed to be conformant to n3000, except for
   redeclarations
 - carries_dependency - currently ignored (this is an optimization hint)

llvm-svn: 89543