Attached patch adds install zabbix iclude files:

common.h
log.h
module.h
sysinc.h
zbxjson.h
zbxtypes.h 

in $(includedir}/zabbix-1.0. and pkgconfig zabbix-1.0.pc file.

"1.0" in this case it is API version but IMO it could be used here zabbix major version like "3.4" or "4.0".
In zabbix-1.0.pc are provided as well zabbix loadable modules base directory, external scripts path alert scripts path so other packages may query over pkgconfig where to install modules and scips to be ready to use by zabbix.