fix runqlen.py with 4.15 kernel
fix runqlen.py with 4.15 kernel

The following kernel commit changes linux_src:kernel/sched/sched.h
struct cfs_rq structure:

```
commit 1ea6c46a23f1213d1972bfae220db5c165e27bba
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Sat May 6 15:59:54 2017 +0200

    sched/fair: Propagate an effective runnable_load_avg

    The load balancer uses runnable_load_avg as load indicator. For
    !cgroup this is:

      runnable_load_avg = \Sum se->avg.load_avg ; where se->on_rq

    That is, a direct sum of all runnable tasks on that runqueue. As
    opposed to load_avg, which is a sum of all tasks on the runqueue,
    which includes a blocked component.
...
```

The commit is in kernel 4.15 release and will make current
runqlen.py internal cfs_rq_partial structure not syncing with the kernel one.
As a result, runqlen.py will produce incorrect results on 4.15.

This patch attempts to solve this issue by compiling a bpf program,
which accesses one of fields introduced by the above commit.
The successful compilation will indicate that we should amend
the cfs_rq_partial structure.

Signed-off-by: Yonghong Song <e76892bbe783db2f627de1232e139db4de43da60@fb.com>

iovisor/bcc,tuxology/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc,mcaleavya/bcc,brendangregg/bcc,iovisor/bcc,mcaleavya/bcc,tuxology/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,mcaleavya/bcc,iovisor/bcc,iovisor/bcc,mcaleavya/bcc,tuxology/bcc