Our CI picked up some issues with clang and some flags. I thought that it was intermittent but it does not look like it:

https://dev.azure.com/scikit-learn/scikit-learn/_build/results?buildId=28285&view=logs&j=e6d5b7c0-0dfd-5ddf-13d5-c71bebf56ce2&t=83107d01-18db-5293-bb0f-49ac2bf2f625&l=1092