Makefile: cross compile generator with the build machine toolchain.
Makefile: cross compile generator with the build machine toolchain.

This fixes a problem when cross compiling that generators and other
helper binaries should be compiled against the build machine (not the
host machine) since they are meant to be executed.

newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat