Fix compilation on MSVC 2008

Fix compilation on MSVC 2008

We are using std::lower_bound on a vector where the item we search for
is of a different type than the items in the container. MSVC 2008's STL
is very happy to check all sorts of constraints and also compare the order
of items within the container. That means it tries to call the compare function
not only with the key we're searching and one item but also two items from
the container. The existing compare function can't satisfy that constraint,
so instead we'll go back to the old approach of a proper functor that
operates outside of the class scope, in order to build with older compilers.

That functor now offers all necessary overloads.

Task-number: QTBUG-38873
Change-Id: I6f350106f98cb03a4ff7e1671a84e67f629cedd3
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>