dtdocbook: make it build under autotools

Remove a pile of old SGML stuff we no longer need in dtdocbook since
we use NSGMLS.

Use some TCL macros from m4/tcl.m4 to loacate and use information in
the tclConfig.sh script installed with TCL.  I had to modify it to
export TCL_INCLUDE_SPEC, which was present but not imported.

cde/programs/dtdocbook/instant/Makefile.am

@@ -2,33 +2,13 @@ MAINTAINERCLEANFILES = Makefile.in
 
 noinst_PROGRAMS = instant
 
-instant_CFLAGS = -I../lib/tptregexp -I$(SVCSRC)/DtUtil2
+instant_CFLAGS = -I../lib/tptregexp $(DT_INCDIR)
 
-instant_LDADD = $(LIBSVC) $(LIBTT) $(XTOOLLIB) ${X_LIB} -L../lib/tptregexp \
-		-ltptregexp -lm
-if LINUX
-instant_CFLAGS += -I/usr/include/tcl
-instant_LDADD += -ltcl
-endif
+instant_LDADD = $(DTCLIENTLIBS) $(XTOOLLIB) -L../lib/tptregexp \
+		-ltptregexp
 
-if FREEBSD
-instant_CFLAGS += -I/usr/local/include/tcl8.6
-instant_LDADD += -ltcl86
-endif
-
-if OPENBSD
-instant_CFLAGS += -I/usr/local/include/tcl8.6
-instant_LDADD += -ltcl86
-endif
-
-if NETBSD
-instant_CFLAGS += -I/usr/pkg/include/tcl
-instant_LDADD += -ltcl86
-endif
-
-if SOLARIS
-instant_LDADD += -lsocket -lnsl -lgen
-endif
+instant_CFLAGS += @TCL_INCLUDE_SPEC@
+instant_LDADD += @TCL_LIB_SPEC@
 
 instant_SOURCES = main.c util.c info.c translate.c traninit.c tranvar.c \
 		  tables.c browse.c