cirrus scripts could use make -k

[Peter Eisentraut]

I would find it useful if the cirrus scripts used make -k (and ninja -k) 
to keep building everything in the presence of errors.  For example, I 
once had some issue in code that caused a bunch of compiler warnings on 
Windows.  The cirrus build would only show me the first one, then I had 
to fix, reupload, see the next one, etc.  Are there any drawbacks to 
using these options in this context?