cc/gcc: suffle options around

Move options around so it feels more organised.
Add comments to separate groups of related options.

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

# Linux kernel options

config KERNEL_linux

    select KERNEL_SUPPORTS_SHARED_LIBS

    help

      Build a toolchain targeting systems running Linux as a kernel.