Merge branch 'selftests-bpf-fix-expression-result-unused-warnings-with-icecc'

Ilya Leoshkevich says:

====================
selftests/bpf: Fix "expression result unused" warnings with icecc

v3: https://lore.kernel.org/bpf/20250827194929.416969-1-iii@linux.ibm.com/
v3 -> v4: Go back to the original solution (Yonghong, Alexei).

v2: https://lore.kernel.org/bpf/20250827130519.411700-1-iii@linux.ibm.com/
v2 -> v3: Do not touch libbpf, explain how having two function
          declarations works (Andrii).
          Fix bpf-gcc build (CI).

v1: https://lore.kernel.org/bpf/20250508113804.304665-1-iii@linux.ibm.com/
v1 -> v2: Annotate bpf_obj_new_impl() with __must_check (Alexei).
          Add an explanation about icecc.

I took another look at the "expression result unused" warnings I've
been seeing, and it turned out that the root cause was the icecc
compiler wrapper and what I consider a clang bug. Back then I've
reported that the problem was reproducible with plain clang, but now
I see that it was clearly a mixup, sorry about that.

The solution is to add a few awkward (void) casts. I've added a
detailed explanation of why they are helpful to the commit message.
====================

Link: https://patch.msgid.link/20250829030017.102615-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>