configure/Makefiles: add checks for Xmu, Xext, and Xdmcp

We also remove sun pro specific options, and do some general cleanup
as well as remove hardcoded library refs like -lXm, -lXext, etc...

cde/programs/dtappbuilder/src/ab/Makefile.am

@@ -47,7 +47,7 @@ SOURCES.msg = \
 dtbuilder_LDADD = ../libABil/libABil.a  ../libABobjXm/libABobjXm.a  \
         ../libABobj/libABobj.a ../libAButil/libAButil.a \
         $(LIBWIDGET) $(LIBTERM) $(LIBHELP) $(LIBSVC) \
-        $(LIBTT) $(LIBXIN) -lUil $(MRESOURCELIB) -lXm $(XTOOLLIB) ${X_LIB} \
+        $(LIBTT) $(LIBXIN) -lUil $(MRESOURCELIB) $(XTOOLLIB) ${X_LIB} \
         $(UTILLIB) -lm
 
 dtbuilder_CFLAGS = -DPIXMAP_WORKAROUND $(ABINCLUDES)