I am having a similar issue. I checked that LLVM is in my path and rebuilt in Atom using "Menu: PlatformIO > Rebuild C/C++ Project Index (Autocomplete, Linter)" THEN closed Atom manually and re-opened and I STILL get "[Linter] Error running clang". When I check the developed debugger it says:
Error running clang Error: Failed to spawn command
clang. Make sure
clang is installed and on your PATH
at process.tickCallback (internal/process/nexttick.js:103:7)
But I already checked that clang is on the path!! What is going wrong here?