perf test: Compile named_threads workload with -O0

perf test: Compile named_threads workload with -O0

The work loop relies on the compiler not optimizing it away, although
named_threads_work is not static for that reason, the compiler could
still do it.

Fix it by compiling without optimization. Also add -fno-inline for
consistency and in case anyone wants to look at callstacks.

Fixes: b5dd510be55e8670 ("perf test: Add named_threads workload")
Closes: https://lore.kernel.org/all/20260609160001.2739E1F00893@smtp.kernel.org
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Reviewed-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>