[CMake] find_package with COMPONENTS never honors REQUIRED

[George PF]

> The documentation is intriguing about REQUIRED COMPONENTS interaction....

That's... one way to put it.
 
> "A package-specific list of required components may be listed after the
> ``COMPONENTS`` option (or after the ``REQUIRED`` option if present).
> Additional optional components may be listed after
> ``OPTIONAL_COMPONENTS``."
>  
> and....
>  
> "Available components and their influence on
> whether a package is considered to be found are defined by the target
> package."
>  
> and later on:
>  
> "In Config mode ``find_package`` handles ``REQUIRED``, ``QUIET``, and
> ``[version]`` options automatically but leaves it to the package
> configuration file to handle components in a way that makes sense
> for the package.  The package configuration file may set
> ``<package>_FOUND`` to false to tell ``find_package`` that component
> requirements are not satisfied."
>  
> So it is possible that the failure behavior when specifying COMPONENTS is up to the module...

I admit I was not reading the docs in that depth, but REQUIRED can only mean one thing and should
not need second guessing the documentation. Sadly, someone thought otherwise.

> Do you see this only with Qt or do other packages with components (may be Boost) behave like this?
> I guess that Qt5 should be running in config mode, whereas boost must be in module mode though. 

I was debugging an older cmake project and wondered why it was not finding the non-standard Qt location, 
that's when I stumbled upon this issue.

GPF