samples/bpf: Fix compilation failure for samples/bpf on LoongArch Fedora

When building the latest samples/bpf on LoongArch Fedora

     make M=samples/bpf

There are compilation errors as follows:

In file included from ./linux/samples/bpf/sockex2_kern.c:2:
In file included from ./include/uapi/linux/in.h:25:
In file included from ./include/linux/socket.h:8:
In file included from ./include/linux/uio.h:9:
In file included from ./include/linux/thread_info.h:60:
In file included from ./arch/loongarch/include/asm/thread_info.h:15:
In file included from ./arch/loongarch/include/asm/processor.h:13:
In file included from ./arch/loongarch/include/asm/cpu-info.h:11:
./arch/loongarch/include/asm/loongarch.h:13:10: fatal error: 'larchintrin.h' file not found
         ^~~~~~~~~~~~~~~
1 error generated.

larchintrin.h is included in /usr/lib64/clang/14.0.6/include,
and the header file location is specified at compile time.

Test on LoongArch Fedora:
https://github.com/fedora-remix-loongarch/releases-info

Signed-off-by: Haoran Jiang <jianghaoran@kylinos.cn>
Signed-off-by: zhangxi <zhangxi@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250425095042.838824-1-jianghaoran@kylinos.cn

Author: Haoran Jiang

samples/bpf/Makefile

@@ -376,7 +376,7 @@ $(obj)/%.o: $(src)/%.c
 	@echo "  CLANG-bpf " $@
 	$(Q)$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(BPF_EXTRA_CFLAGS) \
 		-I$(obj) -I$(srctree)/tools/testing/selftests/bpf/ \
-		-I$(LIBBPF_INCLUDE) \
+		-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
 		-D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
 		-D__TARGET_ARCH_$(SRCARCH) -Wno-compare-distinct-pointer-types \
 		-Wno-gnu-variable-sized-type-not-at-end \