Add a build script to compile bpf source code. A program in restricted
C is compiled into an object file. Object file is converted to BPF
skeleton [0] header file.
If build with custom meson build rule, the target header will reside in
build/ directory (not in source tree), e.g the path for socket_bind:
`build/src/core/bpf/socket_bind/socket-bind.skel.h`
Script runs the phases:
* clang to generate *.o from restricted C
* llvm-strip to remove useless DWARF info
* bpf skeleton generation with bpftool
These phases are logged to stderr for debug purposes.
To include BTF debug information, -g option is passed to clang.
[0] https://lwn.net/Articles/806911/
cf4f9a57f2