Hm…
Where are your source files located? (complete path)
/home/micha/Dokumente/PlatformIO/Projects/Lint/ etc.
So nothing special here… I’m running out of ideas… 
Thank you for your attempts. 
Loong time ago…
I found a workaround now at least: add the -fms-extensions option to the build_flags to get rid of these specific clang errors. One is hiding potential error causes with this, though.