accel/tcg: Declare missing cpu_loop_exit*() stubs

cpu_loop_exit*() functions are declared in accel/tcg/cpu-exec-common.c,
and are not available when TCG accelerator is not built. Add stubs so
linking without TCG succeed.

Problematic files:

- hw/semihosting/console.c in qemu_semihosting_console_inc()
- hw/ppc/spapr_hcall.c in h_confer()
- hw/s390x/ipl.c in s390_ipl_reset_request()
- hw/misc/mips_itu.c

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210117164813.4101761-5-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/stubs/tcg-stub.c

@@ -28,3 +28,13 @@ void *probe_access(CPUArchState *env, target_ulong addr, int size,
      /* Handled by hardware accelerator. */
      g_assert_not_reached();
 }
+
+void QEMU_NORETURN cpu_loop_exit(CPUState *cpu)
+{
+    g_assert_not_reached();
+}
+
+void QEMU_NORETURN cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc)
+{
+    g_assert_not_reached();
+}