xen/arm: traps: Fix MISRA C 2012 Rule 8.4 violation
Add the function prototype of show_stack() in <asm/processor.h> header file
so that it is visible before its definition in traps.c.
Although show_stack() is referenced only in traps.c, it is declared with
external linkage because, during development, it is often called also by
other files for debugging purposes. Declaring it static would increase
development effort. Add appropriate comment
Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>