perf bench syscall: Fix __NR_execve undeclared build error

The __NR_execve definition for i386 was deleted by mistake
in the commit ece7f7c0 ("perf bench syscall: Add fork
syscall benchmark"), add it to fix the build error on i386.

Fixes: ece7f7c0

 ("perf bench syscall: Add fork syscall benchmark")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: loongson-kernel@lists.loongnix.cn
Closes: https://lore.kernel.org/all/CA+G9fYvgBR1iB0CorM8OC4AM_w_tFzyQKHc+rF6qPzJL=TbfDQ@mail.gmail.com/
Link: https://lore.kernel.org/r/1684480657-2375-1-git-send-email-yangtiezhu@loongson.cn
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>