MDEV-20246 Error compiling PAM plugin.

Ignore the setreuid() return here.

plugin/auth_pam/auth_pam_tool.c

@@ -70,7 +70,7 @@ int main(int argc, char **argv)
   int res;
   char a_buf[MYSQL_USERNAME_LENGTH + 1 + 1024];
 
-  setreuid(0, 0);
+  (void) setreuid(0, 0);
 
   if (read(0, &field, 1) < 1)
     return -1;