runqslower build failed on Debian9

[Liu Yiding <liuyd.fnst@xxxxxxxxxxxxxx>]

Hi, Andrii.

I noticed you had added runqslower tool to tools/bpf, so drop this 
problem to you.


Now i failed to run bpf tests since i can't build runqslower.

Testing env: "Debian GNU/Linux 9 (stretch)"

kernel: 5.6.0-rc5

gcc: gcc 6.3

clang: clang-11.


Description: Build runqslower failed due to build error "incomplete 
type" and libbpf show unsupported BTF_KIND:7.

Whole build log please see the attatchment.


Error info

```

root@vm-snb-144 ~/linus/tools/bpf# make

Auto-detecting system features:
...                        libbfd: [ on  ]
...        disassembler-four-args: [ OFF ]

[snip]

  INSTALL  bpftool
  LINK     bpf_asm
  GEN      vmlinux.h
libbpf: unsupported BTF_KIND:7    (Many unsupported errors)
libbpf: unsupported BTF_KIND:7
libbpf: unsupported BTF_KIND:7

[snip]

(Many incomplete type errors)

.output/vmlinux.h:8401:18: error: field has incomplete type 'struct 
idt_bits'
        struct idt_bits bits;
                        ^
.output/vmlinux.h:8396:8: note: forward declaration of 'struct idt_bits'
struct idt_bits;
       ^
.output/vmlinux.h:8598:21: error: field has incomplete type 'struct 
trace_entry'
        struct trace_entry ent;
                           ^
.output/vmlinux.h:8595:8: note: forward declaration of 'struct trace_entry'
struct trace_entry;
       ^
.output/vmlinux.h:9006:25: error: array has incomplete element type 
'struct cyc2ns_data'
        struct cyc2ns_data data[2];
                               ^
.output/vmlinux.h:3669:8: note: forward declaration of 'struct cyc2ns_data'
struct cyc2ns_data;
       ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
Makefile:56: recipe for target '.output/runqslower.bpf.o' failed
make[1]: *** [.output/runqslower.bpf.o] Error 1
Makefile:119: recipe for target 'runqslower' failed
make: *** [runqslower] Error 2

```


--
Best Regards.
Liu Yiding

Attachment: build-log.gz
Description: application/gzip