[DRAFT Proposal] Improving CMake scripts for getting libbcc with FetchContent

## Motivation

Now for building and getting libbcc as a shared or static library for different architectures, I have to build it first, then install it, and then search for library files in the specified directories for using in my project. If FetchContent is used, it turns out that the library is not designed for using with this. This is bad in the case when I want to use the library in my project with cross-compilation for embedded systems. For example, in my project I use bcc as a JIT interpreter for BPF programs, and I think it would be convenient to use the library using FetchContent introduced in CMake.