[CMake] --find-package option fails with some of the Qt5 components

[Stephen Kelly]

Alan W. Irwin wrote:

> Hi Steve:
> 
> PLplot not only CMake exports its libraries but also provides library
> information in pkg-config form for our users that prefer that form.
> Therefore, for this component of our install I need to collect
> explicit compile and link flags for Qt5, and it appears to me the best
> way to do that is to run cmake with the --find-package option.

The cmake --find-package feature is Alex Neundorf's department. I don't 
really know anything about it.

Thanks,

Steve.