Ninja generator breaks when creating archives with GNU 'ar' in Windows
The variation to the above mentioned issue is the usage of Clang and GNU 'ar' instead of of GCC and GNU 'ar'.
Based on what I can tell from the second issue, the fix was to detect if GCC was present and a forward slash was to be used instead. If the same thing can be applied to clang, it would be useful. Or maybe instead of it being compiler dependent, it should just see if it's GNU 'ar' since that's the common denominator.
I've tested this on cmd.exe and Git for Windows bash shell.