Merge branch 'samples: bpf: fix build issues with Clang/LLVM'

Alexander Lobakin says:

====================

Samples, at least XDP ones, can be built only with the compiler used
to build the kernel itself.
However, XDP sample infra introduced in Aug'21 was probably tested
with GCC/Binutils only as it's not really compilable for now with
Clang/LLVM.
These two are trivial fixes addressing this.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>