Fix use of CompEnd predicate to be standards conforming

The existing CompEnd predicate does not define a strict weak order as required
by the C++03 standard; therefore, its use as a predicate to std::upper_bound
is invalid. For a discussion of this issue, see
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#270

This patch replaces the asymmetrical comparison with an iterator adaptor that
achieves the same effect while being strictly standard-conforming by ensuring
an apples-to-apples comparison.

llvm-svn: 127462