ubuntu_bpf failed to build on 5.0 OEM-OSP1

[Po-Hsu Lin]

Test build failed with:
  undefined reference to `RET_IF'

make: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests'
stderr:
/bin/sh: 1: llvm-readelf: not found
/bin/sh: 1: llvm-readelf: not found
Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'
Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' differs from latest version at 'include/uapi/linux/if_link.h'
test_select_reuseport.c: In function 'cleanup_per_test':
test_select_reuseport.c:619:3: warning: implicit declaration of function 'RET_IF' [-Wimplicit-function-declaration]
   RET_IF(err, "reset elem in result_map",
   ^~~~~~
/tmp/ccvA9FfO.o: In function `main':
test_select_reuseport.c:(.text.startup+0x8ad): undefined reference to `RET_IF'
test_select_reuseport.c:(.text.startup+0x8ed): undefined reference to `RET_IF'
collect2: error: ld returned 1 exit status
make[1]: *** [/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/test_select_reuseport] Error 1
make: *** [all] Error 2

Possible fix:
https://lists.ubuntu.com/archives/kernel-team/2020-April/108912.html

[Po-Hsu Lin (cypressyew)]

Note that this build issue does not exist on Bionic GKE 5.0.0-1034.35:
http://10.246.72.7/5.0.0-1034.35-gcp/bionic-linux-gke-5.0-gke-5.0-5.0.0-f1-micro-ubuntu_bpf/ubuntu_bpf/results/ubuntu_bpf.setup/debug/ubuntu_bpf.setup.DEBUG.html

[Po-Hsu Lin (cypressyew)]

5.0 OEM EOL