CMAKE_FIND_PACKAGE_WARN_NO_MODULE
---------------------------------

Tell find_package to warn if called without an explicit mode.

If find_package is called without an explicit mode option (MODULE,
CONFIG or NO_MODULE) and no Find<pkg>.cmake module is in
CMAKE_MODULE_PATH then CMake implicitly assumes that the caller
intends to search for a package configuration file.  If no package
configuration file is found then the wording of the failure message
must account for both the case that the package is really missing and
the case that the project has a bug and failed to provide the intended
Find module.  If instead the caller specifies an explicit mode option
then the failure message can be more specific.

Set CMAKE_FIND_PACKAGE_WARN_NO_MODULE to TRUE to tell find_package to
warn when it implicitly assumes Config mode.  This helps developers
enforce use of an explicit mode in all calls to find_package within a
project.