Zabbix

....I..... [ZBX-25321] updated libevent m4 macros

This is a hack to begin with, but a hack that didn't work correctly.

The test included the pre-libevent 2.x event.h header and a
post-libevent 2.x header. This broke the detection of the library where
the installed libevent 2.x library _didn't_ provide the event.h compat
header, thus breaking the build.

In the tree we use the libevent 2.x API. Update the link test to use it
as well.