Build failure reported on kubuntu 14.04:
$ make
cc  -O2 -s -Wall -fPIE -pie  -ldl -o userhosts userhosts.c
/tmp/ccVLIqoI.o: In function `dlsym_or_abort.part.0':
userhosts.c:(.text.startup+0x5): undefined reference to `dlerror'
/tmp/ccVLIqoI.o: In function `init':
userhosts.c:(.text.startup+0x42): undefined reference to `dlerror'
userhosts.c:(.text.startup+0x55): undefined reference to `dlsym'
userhosts.c:(.text.startup+0x69): undefined reference to `dlerror'
userhosts.c:(.text.startup+0x7c): undefined reference to `dlsym'
collect2: error: ld returned 1 exit status
make: *** [userhosts] Error 1

Fix's rationale seems to be provide -ldl *after* symbol need becomes known,
so after source code is provided & built.