libc/newlib: fix variables for avr32 headers

Some of the avr32headers related variables are used in different
functions, so have to be declared globally, not locally.

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

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""