Don't force installation of static libgamemodeauto

[chewi]

Defining the library with library rather than both_libraries allows the user to choose which type they want to install using -Ddefault_library.

Closes: #287

[stephanlachnit]

Can you please test that when running default_library= both and default_library=static libgamemode is always only a shared library and only libgamemodeauto is affected? Even then, I think it is sensible to always build libgamemodeauto static as part of the development files. Statically linking it makes perfect sense for distributed binaries of games (and it is really really tiny, it's basically only a dynamic loader for the shared library).

Also setting default_library=static breaks gamemoderun.

[chewi]

I've tested and it is all as you say.

How would you like default_library=static to be handled? Don't install gamemoderun? Emit a warning about that?

[stephanlachnit]

How would you like default_library=static to be handled? Don't install gamemoderun? Emit a warning about that?

Maybe a warning and not installing gamemoderun / building libgamemode at all?

[chewi]

Done that now. Sorry for the wait.

[stephanlachnit]

Thanks, LGTM if the CI passes (cc @afayaz-feral)