Fix build in Fedora and print a confimation of cross compilation.

- Fedora only needs --arch if cross compiling.
  + It's only used to select libdir so i386=i686=i986
- Messages are nice to debug build logs.
.
Everything seems to work unless some other distro broke. Other
distros need to add CMAKE_TOOLCHAIN_FILE or --cross-multilib if
they cross compiled amd64 -> i686.