[PATCH bpf v1] selftests/bpf: Fix selftest build after filter.h update

[Ihor Solodrai <ihor.solodrai@linux.dev>]

Upstream commit 7a1f400ff5e5 ("tools: Ensure tools copy of
linux/filter.h exports the UAPI") caused selftests/bpf build to
fail [1] with:

  In file included from progs/arena_atomics.c:9:
  /codebuild/output/src2365462129/src/actions-runner/_work/bpf/bpf/tools/testing/selftests/bpf/../../../include/linux/filter.h:9:10: fatal error: 'uapi/linux/filter.h' file not found
      9 | #include <uapi/linux/filter.h>
        |          ^~~~~~~~~~~~~~~~~~~~~
  1 error generated.
    CLNG-BPF [test_progs] bind_perm.bpf.o
  make: *** [Makefile:888: /codebuild/output/src2365462129/src/actions-runner/_work/bpf/bpf/tools/testing/selftests/bpf/arena_atomics.bpf.o] Error 1
  make: *** Waiting for unfinished jobs....
    GEN-OBJ  [libarena] libarena.bpf.o
    GEN-SKEL [libarena] libarena.skel.h
  make: Leaving directory '/codebuild/output/src2365462129/src/actions-runner/_work/bpf/bpf/tools/testing/selftests/bpf'
  Process completed with exit code 2.

BPF selftest programs include the tools header directly, but
BPF_CFLAGS only exposes tools/include/uapi. Compiler therefore cannot
resolve the nested UAPI include.

Add tools/include after tools/include/uapi in BPF_CFLAGS. This
preserves the existing UAPI header precedence while allowing tools
headers to include uapi headers.

[1] https://github.com/kernel-patches/bpf/actions/runs/31806678733/job/94787271162

Fixes: 7a1f400ff5e5 ("tools: Ensure tools copy of linux/filter.h exports the UAPI")
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 tools/testing/selftests/bpf/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 384c6e8d9274..c0a73473d14e 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -463,7 +463,7 @@ endif
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
 BPF_CFLAGS = -g -Wall -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)	\
 	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
-	     -I$(CURDIR)/libarena/include				\
+	     -I$(TOOLSINCDIR) -I$(CURDIR)/libarena/include		\
 	     -I$(abspath $(OUTPUT)/../usr/include)			\
 	     -std=gnu11		 					\
 	     -fno-strict-aliasing 					\
-- 
2.55.0