scripts: check for running as root

Running as root is really, really dangerous.

Add a runtime-check that refuses to build if running as root.
Can be overriden with a double switch in the menuconfig.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # Compute sparc-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="${CT_ARCH}64"

     fi

 }