When cross compiling arm64 bpf selftests in x86_64 host, the following
error occur:

progs/loop2.c:20:7: error: incomplete definition of type 'struct
user_pt_regs'

Some archs, like arm64 and riscv, use userspace pt_regs in bpf_tracing.h.
When arm64 bpf selftests cross compiling in x86_64 host, clang cannot
find the arch specific uapi ptrace.h. We can add arch specific header
file directory to fix this issue.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
v1->v2:
- use vmlinux.h directly might lead to verifier fail.
- use source arch header file directory suggested by Andrii Nakryiko.

 tools/testing/selftests/bpf/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 42ffc24e9e71..1ecb6d192953 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile

@@ -12,6 +12,7 @@ BPFDIR := $(LIBDIR)/bpf
 TOOLSINCDIR := $(TOOLSDIR)/include
 BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
 APIDIR := $(TOOLSINCDIR)/uapi
+ARCH_APIDIR := $(abspath ../../../../arch/$(SRCARCH)/include/uapi)
 GENDIR := $(abspath ../../../../include/generated)
 GENHDR := $(GENDIR)/autoconf.h

@@ -294,7 +295,8 @@ MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
 BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
             -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)                   \
-            -I$(abspath $(OUTPUT)/../usr/include)
+            -I$(abspath $(OUTPUT)/../usr/include)                      \
+            -I$(ARCH_APIDIR)