[RFC] perf build: Allow passing extra Clang flags via EXTRA_CLANG_FLAGS

[hupu]

When cross-compiling perf with the BPF option enabled, Clang is used
during the build process. Some environments may require additional
compiler options such as `--sysroot` or custom include paths. This patch
adds a new make variable, `EXTRA_CLANG_FLAGS`, which appends user-specified
options to `CLANG_OPTIONS` during BPF skeleton builds.

Example:

  EXTRA_CLANG_FLAGS="--sysroot=$SYSROOT"
  make perf ARCH=arm64 EXTRA_CLANG_FLAGS="$EXTRA_CLANG_FLAGS"

This enables more flexible cross-compilation setups without modifying
Makefile.perf directly.

Signed-off-by: hupu <hupu.gm@xxxxxxxxx>
---
 tools/perf/Makefile.perf | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 47c906b807ef..b0da7314a0d8 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -1249,6 +1249,11 @@ else
 	$(Q)cp "$(VMLINUX_H)" $@
 endif
 
+# Allow users to specify additional Clang options (e.g. --sysroot)
+# when cross-compiling BPF skeletons, enabling more flexible
+# build configurations.
+CLANG_OPTIONS += $(EXTRA_CLANG_FLAGS)
+
 $(SKEL_TMP_OUT)/%.bpf.o: $(OUTPUT)PERF-VERSION-FILE util/bpf_skel/perf_version.h | $(SKEL_TMP_OUT)
 $(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) $(SKEL_OUT)/vmlinux.h
 	$(QUIET_CLANG)$(CLANG) -g -O2 -fno-stack-protector --target=bpf \
-- 
2.43.0