I've had another look at this and I think I have found where the '-lXp'
comes from.
In xtel's Imakefile we find:
...
#include "Motif.tmpl"
...
#ifdef MOTIF
TOOLKITSRCS= xm.c
TOOLKITOBJS= xm.o
LDLIBS= -LVideotex -lVideotex $(LWIDGETS) $(JPEGLIB) XmClientLibs
$(XPMLIB) $(XTOOLLIB) $(XLIB) $(SYSLIBS) $(EXTRA_LIBRARIES) $(XMEXTRA_LIBS)
...
XmClientLibs is defined in /usr/lib/X11/config/Motif.tmpl from package
xutils-dev:
...
#ifndef XmClientLibs
# define XmClientLibs $(XMLIB) $(XTOOLLIB) $(XPLIB) $(XLIB) $(XMEXTRA_LIBS)
#endif
...
