linux-user: Remove type casts to union type

Casting to a union type is a gcc (and clang) extension. Other compilers
might not support it. This is not a problem today, but the type casts
can be removed easily. Smatch now no longer complains like before:

linux-user/syscall.c:3190:18: warning: cast to non-scalar
linux-user/syscall.c:7348:44: warning: cast to non-scalar

Cc: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

linux-user/syscall.c

@@ -2728,8 +2728,9 @@ static inline abi_long host_to_target_semarray(int semid, abi_ulong target_addr,
 }
 
 static inline abi_long do_semctl(int semid, int semnum, int cmd,
-                                 union target_semun target_su)
+                                 abi_ulong target_arg)
 {
+    union target_semun target_su = { .buf = target_arg };
     union semun arg;
     struct semid_ds dsarg;
     unsigned short *array = NULL;
@@ -3251,8 +3252,7 @@ static abi_long do_ipc(unsigned int call, abi_long first,
          * ptr argument. */
         abi_ulong atptr;
         get_user_ual(atptr, ptr);
-        ret = do_semctl(first, second, third,
-                (union target_semun) atptr);
+        ret = do_semctl(first, second, third, atptr);
         break;
     }
 
@@ -7550,7 +7550,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 #endif
 #ifdef TARGET_NR_semctl
     case TARGET_NR_semctl:
-        ret = do_semctl(arg1, arg2, arg3, (union target_semun)(abi_ulong)arg4);
+        ret = do_semctl(arg1, arg2, arg3, arg4);
         break;
 #endif
 #ifdef TARGET_NR_msgctl