cmake: fix error getting LOCATION property on non-imported target

[Boris-Rasin]

CMake allows getting LOCATION property only on IMPORTED targets:
https://cmake.org/cmake/help/latest/prop_tgt/LOCATION.html

Currently, curl cmake avoids getting LOCATION property on INTERFACE targets only.
With this change, it will avoid getting LOCATION property on all non-imported targets, not only INTERFACE targets.

This is required when both curl and zlib are built in the same CMake project (for example, when build with CMake package manager: https://github.com/scapix-com/cmodule), in which case ZLIB::ZLIB is a normal CMake target (not IMPORTED and not INTERFACE).

[Boris-Rasin]

Any chance this will be accepted?
This doesn't change anything for cases which currently work (IMPORTED or INTERFACE targets).
This only changes behavior for cases which currently fail (regular targets, not IMPORTED and not INTERFACE).

[bagder]

We just need someone who knows something about cmake to approve it!

[jzakrzewski]

The docu suggests that it can be used for not IMPORTED targets but simply reading the description gives me headache. It's a mess that can go wrong quite easily and is basically only provided for compatibility, so I think this PR is a good change.

[bagder]

Thanks, both of you!