Respect BUILD_SHARED_LIBS for libappimage

[amazingakai]

Updates the build setup to respect the BUILD_SHARED_LIBS flag when building libappimage.

• If BUILD_SHARED_LIBS is On, builds a shared lib and links to xdg-basedir
• If Off, builds a static lib and embeds xdg-basedir object files directly

Also removes the hardcoded libappimage_static target.

Defaults to shared build.

• Added privately linked dependencies to cmake/imported_dependencies.cmake used when building statically.

[TheAssassin]

Your comment makes it sound like this was, I don't know, a standard option or something that already existed but had a bug or similar. What's the motivation for this addition? It clearly adds some complexity, so I feel there needs to be some justification.

[amazingakai]

Your comment makes it sound like this was, I don't know, a standard option or something that already existed but had a bug or similar. What's the motivation for this addition? It clearly adds some complexity, so I feel there needs to be some justification.

Currently libappimage is always built as a SHARED library, and libappimage_static is neither installed nor exported as a proper STATIC target (please correct me if I'm wrong here), so there is no way to link to it directly. By default both static and shared variants are built, which most users don't need and which adds unnecessary overhead. The two target setup (libappimage/libappimage_static) is also non-standard and adds extra work for downstream users.

I needed a static build and had no straightforward way to get it without custom CMake logic to decide which target to link to based on the environment. This change replaces the two-target setup with the standard BUILD_SHARED_LIBS option, so consumers can choose static or shared builds from the same target without extra hacks.

[amazingakai]

ping