Use ZLIB_LIBS when linking libmysqlclient_r (Bug #6418)

libmysql_r/Makefile.am:
  Make sure we link against zlib

libmysql_r/Makefile.am

@@ -22,7 +22,7 @@
 
 target = libmysqlclient_r.la
 target_defs = -DDONT_USE_RAID -DMYSQL_CLIENT @LIB_EXTRA_CCFLAGS@
-LIBS = @LIBS@ @openssl_libs@
+LIBS = @LIBS@ @ZLIB_LIBS@ @openssl_libs@
 
 INCLUDES = @MT_INCLUDES@ \
 	   -I$(top_srcdir)/include $(openssl_includes) @ZLIB_INCLUDES@