build: linkSystemLibrary should abstract over multiple sources of libraries

[Sahnvour]

Following #3447

This comes from the fact that on Windows, we may want to use libraries obtained through vcpkg or conan for example. We can also imagine a daemon to help the user find a manually installed lib.

Citing @andrewrk

The use case we are trying to solve right now is to have a build script API that helps applications link against system libraries, on all platforms. Given that this is the goal, and that linking against a system library may want to take advantage of vcpkg on Windows, I think that we may need to make the linkSystemLibrary API a bit more complicated, in order to gain the ability to fully specify what library the application wants to link against, by allowing the build script to specify multiple names.

artifact.linkSystemLibrary2(.{
    .so_name = "gdk-3",
    .pkgconf_name = "gdk-3.0",
    .vcpkg_name = "gdk",
});

These fields would all default to null and potentially have heuristics for guessing names of other things based on each other. In the status quo API, it's essentially so_name that is the parameter to linkSystemLibrary and the pkgconf_name is guessed based on heuristics.

[nektro]

the upcoming release of https://github.com/nektro/zigmod solves this. example zig.mod

name: my-app
main: src/main.zig
dependencies:
- type: system_lib
  path: gdk
  only_os: windows
- type: system_lib
  path: gdk-3
  except_os: windows

this would then use the already existing linkSystemLibrary function to link gdk when on Windows and gdk-3 otherwise.