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>

 # m68k specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_CPU

 ##

 ## help The m68k architecture