No longer rely on an external tool to build the llvm component layout.
Instead, leverage the existing `add_llvm_componentlibrary` cmake function and
introduce `add_llvm_component_group` to accurately describe component behavior.
These function store extra properties in the created targets. These properties
are processed once all components are defined to resolve library dependencies
and produce the header expected by llvm-config.
Differential Revision: https://reviews.llvm.org/D90848
This change moves elfabi related code to llvm/InterfaceStub library
so it can be shared by multiple llvm tools without causing cyclic
dependencies.
Differential Revision: https://reviews.llvm.org/D85678
