Merge branch 'CO-RE relocation selftests fixes'

Andrii Nakryiko says:

====================

Lorenz Bauer noticed that core_reloc selftest has two inverted CHECK()
conditions, allowing failing tests to pass unnoticed. Fixing that opened up
few long-standing (field existence and direct memory bitfields) and one recent
failures (BTF_KIND_FLOAT relos).

This patch set fixes core_reloc selftest to capture such failures reliably in
the future. It also fixes all the newly failing tests. See individual patches
for details.

This patch set also completes a set of ASSERT_xxx() macros, so now there
should be a very little reason to use verbose and error-prone generic CHECK()
macro.

v1->v2:
  - updated bpf_core_fields_are_compat() comment to mention FLOAT (Lorenz).

Cc: Lorenz Bauer <lmb@cloudflare.com>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>