Diagnose UnresolvedLookupExprs that resolve to instance members in static methods

During the initial template parse for this code, 'member' is unresolved
and we don't know anything about it:

  struct A { int member };
  template <typename T>
  struct B : public T {
    using T::member;
    static void f() {
      (void)member; // Could be static or non-static.
    }
  };
  template class B<A>;

The pattern declaration contains an UnresolvedLookupExpr rather than an
UnresolvedMemberExpr because `f` is static, and `member` should never be
a field. However, if the code is invalid, it may become a field, in
which case we should diagnose it.

Reviewers: rjmccall, rsmith

Differential Revision: http://reviews.llvm.org/D6700

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@250592 91177308-0d34-0410-b5e6-96231b3b80d8