Yes, the last line is for CI. It just runs the tool as a simple check that it built correctly. Cross-compilation does not work with Core RT anyway, so we can assume that you are always building for the host platform.
I remember I had a big fight with dot.net a year or two back, and gave up - but last time I checked the only thing I found missing was a bundler (like warp). And somewhat inconsistent/unclear documentation on how to make a stand alone build. But I did eventually manage to build "Hello, world!" on Linux and run it on windows as a proof of concept.
Huh? I was sure I tested that after an announcement in... November? But it's supposed to have been supported a while longer? Eg: https://www.hanselman.com/blog/SelfcontainedNETCoreApplicati...
Perhaps a warp limitation?