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>

 This is a somewhat ordered TODO list:

 Recurring tasks:

 - update versions for every tools...

 - update and/or upgrade all samples

 Non-recurring tasks:

 - update newlib (for enhanced bare metal)

   - confirm existing implementation on targets other than AVR32

   - try to make it generic, will help for uClibc++

 - multilib

 - Cygwin target (needs newlib)

   - so we can build toolchains that generate code for Windows/Cygwin

 - uClibc++

   - see newlib, above

 - uClinux

   - check whether we can use newlib under uClinux (?)