Support libcurl < 7.38 for Kerberos authentification

Zabbix 4.4.0 supports Kerberos auth in HTTP agent items and Web-scenarios, but it supports libcurl since 7.38 which is not available in RHEL 7 and CentOS 7. These operating systems have 7.29 version, where it is possible to use CURLAUTH_GSSNEGOTIATE constant instead of CURLAUTH_NEGOTIATE: https://curl.haxx.se/libcurl/c/symbols-in-versions.html