Enable fileinfo extension

It's on a Centos 7, PHP 5.5.38

I thought the fileinfo was enabled by default, but phpinfo() shows below:

'./configure' **'--disable-fileinfo'** '--disable-opcache' '--enable-bcmath' '--enable-calendar' '--enable-ftp' '--enable-gd-native-ttf' '--enable-libxml' '--enable-mbstring' '--enable-pdo=shared' '--enable-soap' '--enable-sockets' '--enable-zip' '--prefix=/usr/local' '--with-apxs2=/usr/local/apache/bin/apxs' '--with-curl=/opt/curlssl/' '--with-freetype-dir=/usr' '--with-gd' '--with-imap=/opt/php_with_imap_client/' '--with-imap-ssl=/usr' '--with-jpeg-dir=/usr' '--with-kerberos' '--with-libdir=lib64' '--with-libxml-dir=/opt/xml2' '--with-libxml-dir=/opt/xml2/' '--with-mcrypt=/opt/libmcrypt/' '--with-mysql=/usr' '--with-mysql-sock=/var/lib/mysql/mysql.sock' '--with-mysqli=/usr/bin/mysql_config' '--with-openssl=/usr' '--with-openssl-dir=/usr' '--with-pcre-regex=/opt/pcre' '--with-pdo-mysql=shared' '--with-pdo-sqlite=shared' '--with-pic' '--with-png-dir=/usr' '--with-xpm-dir=/usr' '--with-zlib' '--with-zlib-dir=/usr'

So how do I enable this fileinfo?

The current extension folder doesn't have fileinfo.so, so I don't know what I need to do now to enable this.