Introduce infrastructure for cross-compiling Fedora kernels
    
      Intended to assist building for secondary architectures like ppc64, s390x,
      and arm.
    
      To use, create an .src.rpm using "fedpkg srpm" and then run
      "rpmbuild --rebuild --with cross --without perf --without tools \
        kernel*.src.rpm" to cross compile. This requires binutils and gcc
      packages named like %_target_cpu, which all but powerpc64 currently provides
      in rawhide/F-19. Can't (currently) cross compile perf or kernel-tools, since
      libc is missing from the cross environment.