libbpf: add bpf_core_type_matches() helper macro

This patch finalizes support for the proposed type match relation in libbpf by
adding bpf_core_type_matches() macro which emits TYPE_MATCH relocation.

Clang support for this relocation was added in [0].

  [0] https://reviews.llvm.org/D126838



Signed-off-by: Daniel Müller <deso@posteo.net&gt;¬>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org&gt;¬>
Link: https://lore.kernel.org/bpf/20220628160127.607834-7-deso@posteo.net¬