[boost] [build] Bootstrap failures in Appveyor CI

Subject: [boost] [build] Bootstrap failures in Appveyor CI
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-04-12 21:04:27

Hi,

I'm seeing multiple Appveyor job failures at bootstrap stage, here's an 
example:

https://ci.appveyor.com/project/Lastique/winapi/build/job/qnu5dhfcpjx3vh1y

The code did not change for quite a while and it was passing before. It 
first failed after the jobs were triggered by the 1.70 tag. Only some of 
the jobs have failed, and after I re-ran the jobs, a different set of 
jobs failed the second time.

Is this something related to Boost.Build or superproject?