make samples/bpf/ using gcc instead of clang/llvm

From: Joel Fernandes
Date: Wed Jan 27 2016 - 00:52:01 EST

Hi Brendan, Alexei,

I noticed your patch fixing the $subject issue.

However, I still see make samples/bpf/ using gcc instead of clang.

Here's a verbose kbuild output of make samples/bpf/. My kernel version
is 4.4. It looks to me like Kbuild is ignoring the Makefile in
samples/bpf/. Let me know if you spot anything of the ordinary?

make KBUILD_VERBOSE=1 samples/bpf/
-f /home/joel/data/repo/linux-4.4/scripts/ obj=samples/bpf
(cat /dev/null; ) > samples/bpf/modules.order
gcc -Wp,-MD,samples/bpf/.test_verifier.o.d -Isamples/bpf -Wall
-Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer
-std=gnu89 -I/home/joel/data/repo/linux-4.4/./usr/include
-I./usr/include -c -o samples/bpf/test_verifier.o
fatal error: linux/bpf.h: No such file or directory
#include <linux/bpf.h>
compilation terminated.
make[2]: *** [samples/bpf/test_verifier.o] Error 1