/usr/lib64/libIrrlicht.so.1.8.4 in irrlicht-1.8.4-1.fc28.6.x86_64 and /usr/lib64/libIrrXML.so.1.8.4 in irrXML-1.8.4-1.fc28.6.x86_64 have not been linked with the standard Fedora linker flags (LDFLAGS) from redhat-rpm-config. I tried to fix this, but had to back out my changes because setting LDFLAGS from the RPM spec file overrides the linked libraries as well, resulting in serious underlinking (which is not detected because the linker flag -Wl,-z,defs is not used). See https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/master/f/buildflags.md for information on RPM macros and environment variables provided by the build environment.
Fixed in rawhide (irrlicht-1.8.4-7.fc29) and F28 (irrlicht-1.8.4-7.fc28).