Turn COMPILER_VERSION/COMPILER_TYPE make check into a compile-time check
of the clang version

This works around breakage on ^/stable/10 when running installworld from
a ^/stable/10 host where the test wouldn't be compiled on the first
go-around and would be missing when make installworld is run.

MFC after: 1 week
PR: 208703
Reported by: emaste
Sponsored by: Dell EMC Isilon