in Leap 42.2 and Tumbleweed, there's
/usr/lib/mono/{2.0-api,3.5-api,4.0,4.0-api,4.5,4.5-api}/System.Core.dll
in Leap 42.1, there's
/usr/lib/mono/{2.0,3.5,4.0,4.5}/System.Core.dll
all these dlls were placed in mono-devel.
So Leap 42.1 don't need a build fix. but 42.2 does.
The problems left is:
* why openSUSE Leap 42.2 standard repository builds.