There are insufficient headers in tools/include to satisfy building BPF
programs and their header dependencies. Add the system include paths
from the non-BPF clang compile so that these headers can be found.

This code was taken from:

  tools/testing/selftests/bpf/Makefile

Committer notes:

Had to adjust the '#ifndef NO_BPF_SKEL' to '#ifdef BUILD_BPF_SKEL' as
reverted that build BPF skels by default.

Also cope with the addition of -I$(srctree)/tools/include/uapi done by
Yang Jihong so that we prefer using the kernel sources headers instead
of older ones in the system.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@meta.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Yang Jihong <yangjihong1@huawei.com>
Link: https://lore.kernel.org/lkml/20230506021450.3499232-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>