[Borgbackup] failed to build

[Thomas Waldmann]

> I uninstalled 1.1.18 to replace it with 1.2.1, checked all
> dependencies were installed, but pip3 is failing and I don't
> know why.
> 
> As it is a long output it is attached as a text file.

Never seen that kind and amount of warnings relating to borg.algorithms 
content.

But the error is close to the end of the log:

error: unknown file type '.pyx' (from 'src/borg/crypto/low_level.pyx')

This is a bit unusual also, because the corresponding .c file should be 
used for a borg release version (so a C compiler is sufficient) and thus 
the .pyx should not be needed to get processed at all (which requires to 
have Cython installed).