Don't use the bundled outdated copy of zlib.

--- Makefile.in.orig	2008-05-08 06:12:33
+++ Makefile.in	2025-09-17 06:39:55
@@ -193,7 +193,7 @@
 
 # Unix source subdirs, where we'll want to run lint and etags:
 # This is a legacy variable from b4 Automake
-USOURCE_SUBDIRS = lib zlib diff src
+USOURCE_SUBDIRS = lib diff src
 # All other subdirs:
 SUBDIRS = $(USOURCE_SUBDIRS) man doc contrib tools \
 	windows-NT os2 emx vms
--- src/Makefile.in.orig	2008-05-08 06:12:32
+++ src/Makefile.in	2025-09-17 06:46:05
@@ -82,7 +82,7 @@
 	version.$(OBJEXT) vers_ts.$(OBJEXT) watch.$(OBJEXT) \
 	wrapper.$(OBJEXT) zlib.$(OBJEXT)
 cvs_OBJECTS = $(am_cvs_OBJECTS)
-cvs_DEPENDENCIES = ../diff/libdiff.a ../lib/libcvs.a ../zlib/libz.a
+cvs_DEPENDENCIES = ../diff/libdiff.a ../lib/libcvs.a
 binSCRIPT_INSTALL = $(INSTALL_SCRIPT)
 SCRIPTS = $(bin_SCRIPTS)
 DEFAULT_INCLUDES = -I. -I$(top_builddir)@am__isrc@
@@ -206,7 +206,7 @@
 # some namespace hackery going on that maybe shouldn't be.  Long term fix is to
 # try and remove naming ocnflicts and fix Automake to allow particular includes
 # to be attached only to particular object files.  Short term fix is either or.
-INCLUDES = -I$(top_srcdir)/lib -I$(top_srcdir)/diff -I$(top_srcdir)/zlib $(includeopt)
+INCLUDES = -I$(top_srcdir)/lib -I$(top_srcdir)/diff $(includeopt)
 bin_SCRIPTS = cvsbug
 
 # The cvs executable
@@ -285,7 +285,7 @@
 cvs_LDADD = \
 	../diff/libdiff.a \
 	../lib/libcvs.a \
-	../zlib/libz.a
+	-lz
 
 
 # extra clean targets
