Allow stand-alone build of simple example

[dg0yt]

This helps to validate the installed package.

It also shows a benefit of the other change: An in-build ggml::ggml ALIAS enables a uniform link library name regardless of ggml being used as a sub-project or via find_package.

[dg0yt]

And the next step is to make CMake config actually work.
Preferably by installing exported configuration.

[slaren]

I am not sure about this. It would be ok to have an example specifically for this purpose, but just randomly changing one of the examples to be a separate project, without any documentation or explanation in the code, is just going to be confusing.

[ggerganov]

Maybe for now just add the ggml::ggml alias and don't change the example?

[dg0yt]

Well, I just use this example to validate the installed cmake config (and in a variation, pkgconfig) of the vcpkg port. Your CI could do the same.

I explicitly tried to find a simple existing example. The additions should not cause much confusion - It is really just very basic CMake, nicely illustrating expected basic usage.

[dg0yt]

Your CI could do the same.

Proof of concept: dg0yt#1

[dg0yt]

• There is no change for in-build experience.
• There is a an extra comment explaining that it can be used in two ways.
• There is a proof of concept how to use it for ggml CI.
  (And it includes fixes for relevant problems.)

What else would be needed to remove concerns?

[dg0yt]

Hm, I expected this to be a no-brainer. I wanted this to be merged before updating the ggml-org ports in vcpkg.

[dg0yt]

... and before upstreaming dg0yt#1.

[ggerganov]

Create a new very trivial example called test-cmake and update its CMakeLists.txt for this purpose. The implementation in test-cmake.cpp can just call ggml_backend_load_all(); and exit.

[dg0yt]

Valid, but obsolete.