[clang] [llvm] [BPF] Generate BTF info using 'btf:type_tag' annotation (PR #91424)

[via llvm-commits]

https://github.com/yonghong-song approved this pull request.

LGTM. The change mostly the same as previous approved patch https://reviews.llvm.org/D145891 except adding some BTF Type Tag V1 handling.
I tried a few examples as well as bpf selftest with both V1 and V2. All tests are passed.

https://github.com/llvm/llvm-project/pull/91424