BIND9 seems to be abusing LDFLAGS here, and it breaks our linker.

--- bin/tests/system/dlzexternal/Makefile.in.orig	2019-06-28 12:33:29 UTC
+++ bin/tests/system/dlzexternal/Makefile.in
@@ -35,7 +35,7 @@ OBJS =
 @BIND9_MAKE_RULES@
 
 CFLAGS =	@CFLAGS@ @SO_CFLAGS@
-SO_LDFLAGS =	@LDFLAGS@ @SO_LDFLAGS@
+SO_LDFLAGS =	@SO_LDFLAGS@
 
 driver.@SO@: ${SO_OBJS}
 	${LIBTOOL_MODE_LINK} @SO_LD@ ${SO_LDFLAGS} -o $@ driver.@O@