Introduce the 'debug-kernel' script to allow developers to
quickly attach a debugger to the QEMU debug remote. The
setting (-s) is already enabled by ./run today when using
QEMU for virtualisation.
If the system is running under QEMU, the debugger
will break in when the script is run. If you add
the -S option to QEMU it will wait for the debugger
to connect before booting the kernel. This allows
you to debug the init/boot process.
Personally I use cgdb instead of gdb, so I opted
to make the debugger used by the script customizable
via an environment variable.
This change also adds -g3 to the kernel build so that
rich debug symbols are available in the kernel binary.
