Michael Dusan 3df0a3a528
macos: add fallback version detection
Fallback to sysctl `kern.osversion` when `kern.osproductversion` is not
available (prior to 10.13.4) .

The mapping from `sw_vers -buildVersion` to `-productVersion` is
formulaic from 10.8 to 10.15 and older is handled with switch.

closes #5119
2020-04-21 18:37:03 -04:00
..
2020-03-08 12:43:32 -04:00