tests/stack_unwind: Avoid inlining and tail-calls

We want the stack trace to show the correct nesting of functions,
so we need to prevent the compiler from in-lining functions or
performing tail-call optimizations.

Add __noinline to prevent inlining. Add another printf in each
function to avoid tail calls.

Signed-off-by: Keith Packard <keithp@keithp.com>