test/bpf: Use Clang to compile BPF unit tests
test/bpf: Use Clang to compile BPF unit tests

The new builtin replacements are only enabled when Clang >=10 is used.
So we need to compile the BPF unit tests with Clang if we want to test
that code.

We need to disable -Wgnu-variable-sized-type-not-at-end to avoid the
following warning:

  In file included from unit-test.c:25:
  In file included from ../../bpf/tests/ipv6_test.h:7:
  ../../bpf/lib/maps.h:123:26: warning: field 'lpm_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
          struct bpf_lpm_trie_key lpm_key;
                                  ^
  1 warning generated.

Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

tklauser/cilium,cilium-team/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium-team/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium