perf config: Update default value for llvm.clang-bpf-cmd-template

The clang bpf cmdline template has defined default value in the file
tools/perf/util/llvm-utils.c, which has been changed for several times.

This patch updates the documentation to reflect the latest default value
for the configuration llvm.clang-bpf-cmd-template.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Drayton <mbd@fb.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Fixes: d35b168c ("perf bpf: Give precedence to bpf header dir")
Fixes: cb763714 ("perf llvm: Allow passing options to llc in addition to clang")
Fixes: 1b16fffa ("perf llvm-utils: Add bpf include path to clang command line")
Link: http://lkml.kernel.org/r/20190607143508.18141-1-leo.yan@linaro.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>