Uniform way to link whole libraries

Use case

Let's say you have 3 libraries and executable

• global register, it defines some storage for plugins that automatically register themselves
• plugin that registers on initialization, can be via __attribute__((constructor)) or static initialization
• user of the register, also links with plugin
• executable that interacts with user but does not know about plugin directly.

There are 3 problems in meson that make it hard to deal with this

1. It is not possible to specify link_whole as part of declare_dependency() call and make executable link with plugin if it is static library.
2. It is not possible to use shared library with link_whole. So if you use library() and let user specify default_library option, you can't consistently use result.
3. Shared libraries are not linked without specifying '-Wl,--no-as-needed'. But this option is not really needed for the whole project, most likely for few plugins only.

Example to demonstrate this behavior.

Proposal

• Add link_whole to declare_dependency(). Semantics is identical to link_with.
• Allow use of shared libraries in link_whole and add '-Wl,--no-as-needed' if shared library is used.
• Or add another option link_always, let it accept both static and shared libraries with behavior described above, and add it to declare_dependency() as well.

Caveat

I did not take any other systems or compilers but Linux/GCC/Clang into consideration. Looking for input.