Add noreturn function attribute

Add noreturn function attribute

Introduce noreturn attribute and attach it to cpu_loop_exit as well as
interrupt/exception helpers for i386. This avoids a bunch of gcc4
warnings.

[ Note that this patch comes with a workaround to include qemu-common.h
even in cases where is currently causes conflicts with dyngen-exec.h.
I've been told that these conflicts will get resolved in the future
(/me will try to have a look as well - as time permits). ]

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6303 c046a42c-6fe2-441c-8c8c-71466251a162