This patch removes the implicit build of all shared libraries a target
depends on. Targets only depend on the respective ABIs instead. This
alleviates the need to locally build complex shared libraries (think of
Qt) when developing applications. Instead, application developers can
use binary depot archives.
The implementation splits the mk/lib.mk file into three files:
- mk/a.mk for building one static library (.lib.a)
- mk/so.mk for building one shared object (.lib.so)
- mk/abi.mk for building one ABI stub (.abi.so)
Furthermore, the commit moves messages and the collection of build
artifacts to var/libdeps, triggers the build of kernel-specific
ld-<kernel>.lib.so, and prunes the lib-dependency tree at ABIs.
Fixes#5061
