Merge branch 'btf-api-extensions'

Andrii Nakryiko says:

====================
This patchset introduces a set of new APIs that make it possible to work with BTF
more effectively (and without involving kernel) for applications like pahole that
need to manipulate .BTF and .BTF.ext data.

Patch #1 changes existing btf__new() API call to only load and initialize
struct btf, while exposing new btf__load() API to attempt to load and validate
BTF in kernel.

Patch #2 adds btf__get_raw_data() API allowing to get access to raw BTF data from
struct btf.

Patch #3 adds similar btf_ext__get_raw_data() API for working with struct btf_ext.

Patch #4 removes not-yet-stable btf__get_strings() API which was added to be able
to test contents of struct btf for btf__dedup(). It's now superseded by raw APIs.

v3->v4:
- formatting fixes
- renamed btf_ext functions/structs to use "setup" language instead of "copy"
- removed btf__get_strings from libbpf.map

v2->v3:
- const void* variants of btf__get_raw_data()
- added btf_ext__get_raw_data()
- removed btf__get_strings() and adapted test_btf.c to use btf__get_raw_data()

v1->v2:
- btf_load() returns just error, not fd
- fix ordering in libbpf.map
====================

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