Define variable CMAKE_FIND_PACKAGE_WARN_NO_MODULE for use by a project
that wants to use an explicit mode in every call to find_package in
order to generate more specific failure messages.  Word the warning
using the new CONFIG and MODULE mode keywords when the minimum required
version of CMake is new enough to have them.  Otherwise word the warning
using the old NO_MODULE mode keyword.

Inspired-by: Alex Neundorf <neundorf@kde.org>