错误的使用：
[root@localhost tacacs+-F4.0.4.26]# gcc
gcc: fatal error: no input files
compilation terminated.
[root@localhost tacacs+-F4.0.4.26]#
正确的示范：
[root@localhost tacacs+-F4.0.4.26]# gcc --version
gcc (GCC) 8.2.1 20180905 (Red Hat 8.2.1-3)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
原因：
gcc不能单独执行，必须要加参数
