[PATCH v2 0/4] Bring back vmlinux.h generation

[Ian Rogers <irogers@google.com>]

Commit 760ebc45746b ("perf lock contention: Add empty 'struct rq' to
satisfy libbpf 'runqueue' type verification") inadvertently created a
declaration of 'struct rq' that conflicted with a generated
vmlinux.h's:

```
util/bpf_skel/lock_contention.bpf.c:419:8: error: redefinition of 'rq'
struct rq {};
       ^
/tmp/perf/util/bpf_skel/.tmp/../vmlinux.h:45630:8: note: previous definition is here
struct rq {
       ^
1 error generated.
```

Fix the issue by moving the declaration to vmlinux.h. So this can't
happen again, bring back build support for generating vmlinux.h then
add build tests.

v2. Rebase on perf-tools-next. Add Andrii's acked-by. Add patch to
    filter out kernels that lack a .BTF section and cause the build to
    break.

Ian Rogers (4):
  perf build: Add ability to build with a generated vmlinux.h
  perf bpf: Move the declaration of struct rq
  perf test: Add build tests for BUILD_BPF_SKEL
  perf build: Filter out BTF sources without a .BTF section

 tools/perf/Makefile.config                    |  4 +++
 tools/perf/Makefile.perf                      | 33 ++++++++++++++++++-
 tools/perf/tests/make                         |  4 +++
 tools/perf/util/bpf_skel/.gitignore           |  1 +
 .../perf/util/bpf_skel/lock_contention.bpf.c  |  2 --
 .../util/bpf_skel/{ => vmlinux}/vmlinux.h     | 10 ++++++
 6 files changed, 51 insertions(+), 3 deletions(-)
 rename tools/perf/util/bpf_skel/{ => vmlinux}/vmlinux.h (90%)

-- 
2.41.0.rc0.172.g3f132b7071-goog