accel/tcg: Restrict cpu_handle_halt() to sysemu

Commit 372579427a5 ("tcg: enable thread-per-vCPU") added the following
comment describing EXCP_HALTED in qemu_tcg_cpu_thread_fn():

    case EXCP_HALTED:
         /* during start-up the vCPU is reset and the thread is
          * kicked several times. If we don't ensure we go back
          * to sleep in the halted state we won't cleanly
          * start-up when the vCPU is enabled.
          *
          * cpu->halted should ensure we sleep in wait_io_event
          */
         g_assert(cpu->halted);
         break;

qemu_wait_io_event() is sysemu-specific, so we can restrict the
cpu_handle_halt() call in cpu_exec() to system emulation.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210912172731.789788-2-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/cpu-exec.c

@@ -588,8 +588,9 @@ static inline void tb_add_jump(TranslationBlock *tb, int n,
 
 static inline bool cpu_handle_halt(CPUState *cpu)
 {
+#ifndef CONFIG_USER_ONLY
     if (cpu->halted) {
-#if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
+#if defined(TARGET_I386)
         if (cpu->interrupt_request & CPU_INTERRUPT_POLL) {
             X86CPU *x86_cpu = X86_CPU(cpu);
             qemu_mutex_lock_iothread();
@@ -597,13 +598,14 @@ static inline bool cpu_handle_halt(CPUState *cpu)
             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
             qemu_mutex_unlock_iothread();
         }
-#endif
+#endif /* TARGET_I386 */
         if (!cpu_has_work(cpu)) {
             return true;
         }
 
         cpu->halted = 0;
     }
+#endif /* !CONFIG_USER_ONLY */
 
     return false;
 }