coroutine: add a macro for the coroutine stack size

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

util/coroutine-sigaltstack.c

@@ -143,7 +143,7 @@ static void coroutine_trampoline(int signal)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = 1 << 20;
+    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineSigAltStack *co;
     CoroutineThreadState *coTS;
     struct sigaction sa;