linux-user: Mark cpu_loop() with noreturn attribute

cpu_loop() never exits, so mark it with QEMU_NORETURN.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-By: Warner Losh <imp@bsdimp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Message-Id: <20211106113916.544587-1-f4bug@amsat.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/user-internals.h

@@ -64,7 +64,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                     abi_long arg5, abi_long arg6, abi_long arg7,
                     abi_long arg8);
 extern __thread CPUState *thread_cpu;
-void cpu_loop(CPUArchState *env);
+void QEMU_NORETURN cpu_loop(CPUArchState *env);
 const char *target_strerror(int err);
 int get_osversion(void);
 void init_qemu_uname_release(void);