Fix PR39458 _LIBCPP_DEBUG breaks heterogeneous compare.

The types/comparators passed to std::upper_bound and std::lower_bound
are not required to provided to provide an operator</comp(...) which
accepts the arguments in reverse order. Nor are the ranges required
to have a strict weak ordering.

However, in debug mode we attempted to check the result of a comparison
with the arguments reversed, which may not compiler.

This patch removes the use of the debug comparator for upper_bound
and lower_bound.

equal_range et al still use debug comparators when they call
__upper_bound and __lower_bound.

See llvm.org/PR39458

llvm-svn: 345434