libAnalysis: Add a case for TypeAliasDecl in CFGRecStmtDeclVisitor.

Neither of the current clients of CFGRecStmtDeclVisitor are doing
anything with typedefs, so I assume type aliases (C++11 "using")
can be safely ignored. This was causing assertion failures in
the analyzer.

<rdar://problem/13228440>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175335 91177308-0d34-0410-b5e6-96231b3b80d8