libev and libevent can be enabled at the same time since version 4.1.0,
thanks to the event lib support refactoring into plugins, which is enabled by
default for unix platform builds (LWS_WITH_EVLIB_PLUGINS=ON):
c6c7ab2b44
In this way, libwebsockets can be compiled with both libev and libevent
support, which is then user-selectable at runtime.
This basically restores the behavior changed by previous commit 27f257e.
Signed-off-by: Luca Pesce <luca.pesce@vimar.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>