config: switch cc with libc in the config order

Some of the compiler options depend on the C library choice, (e.g.
whether core passes are needed).

Since the compiler menu comes before the C library menu, those options
may or may not be visible until the C library is chosen, leading to
either options being visible by the user (thus be puzzling as they would
not apply to his case), or invisible to him (yet again puzzling him).

Invert the order of the compiler and the C library in the menuconfig. It
anyway looks more rational, in the end.

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

# Options specific to crosstool-NG acting as a backend

config IS_A_BACKEND

    string

    option env="CT_IS_A_BACKEND"

config BACKEND

    bool

    default y if IS_A_BACKEND = "y" || IS_A_BACKEND = "Y"

config BACKEND_ARCH

    string

    option env="CT_BACKEND_ARCH"

config BACKEND_KERNEL

    string

    option env="CT_BACKEND_KERNEL"

config BACKEND_LIBC

    string

    option env="CT_BACKEND_LIBC"