stubs: group stubs for user-mode emulation

Some stubs are used for user-mode emulation only; they are not
needed by tools.  Move them out of stubs/.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

user-exec-stub.c

@@ -0,0 +1,34 @@
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qom/cpu.h"
+#include "sysemu/replay.h"
+
+void cpu_resume(CPUState *cpu)
+{
+}
+
+void qemu_init_vcpu(CPUState *cpu)
+{
+}
+
+/* User mode emulation does not support record/replay yet.  */
+
+bool replay_exception(void)
+{
+    return true;
+}
+
+bool replay_has_exception(void)
+{
+    return false;
+}
+
+bool replay_interrupt(void)
+{
+    return true;
+}
+
+bool replay_has_interrupt(void)
+{
+    return false;
+}