local-ci: clang-format hangs in bmcweb sometimes

[Lei YU]

While trying to run local-ci on bmcweb, it's found that the
clang-format hangs sometimes.

Top shows it's consuming 100% CPU on a single core and the memory
consumption is increasing.

Smaple top output:

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 99536 leiyu     20   0 97.067g 0.095t  19520 R 100.0 10.8  10:39.18
clang-format-8

You can see it already takes 10 minutes and it consues nearly 100GiB memory.

It does not happen always, and it seems like it's happening when I run
local-ci for a second time.
E.g. the first local-ci runs OK on a clean repo, and the second
local-ci run hits the above issue.

Is that known issue?