perf: Replace deprecated -target with --target= for Clang

perf: Replace deprecated -target with --target= for Clang

-target has been deprecated since Clang 3.4 in 2013. Use the preferred
--target=bpf form instead. This matches how we use --target= in
scripts/Makefile.clang.

Signed-off-by: Fangrui Song <maskray@google.com>
Acked-by: Yonghong Song <yhs@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: llvm@lists.linux.dev
Cc: Ingo Molnar <mingo@redhat.com>
Cc: bpf@vger.kernel.org
Link: https://github.com/llvm/llvm-project/commit/274b6f0c87a6a1798de0a68135afc7f95def6277
Link: https://lore.kernel.org/r/20230624002708.1907962-1-maskray@google.com
[ resolved a conflict with GEN_VMLINUX_H changes ]
Signed-off-by: Namhyung Kim <namhyung@kernel.org>