bug#61386: [PATCH] cp,mv,install: Disable sparse copy on macOS

[Paul Eggert]

I recall reading somewhere in this thread that a 'split' test was 
failing on macOS because it doesn't let you lseek on /dev/null. I fixed 
that problem here:

https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=aa266f1b3dc4e12acdc46cc0f562adc03c2c0b8f
and fixed some other 'split' issues in adjacent patches, while I was in 
the neighborhood.