Please test it.
diff -Nru isc-dhcp-4.4.1/debian/changelog isc-dhcp-4.4.1/debian/changelog
--- isc-dhcp-4.4.1/debian/changelog 2020-01-22 18:35:14.0 -0300
+++ isc-dhcp-4.4.1/debian/changelog 2020-08-05 23:08:47.0 -0300
@@ -1,3 +1,12 @@
+isc-dhcp (4.4.1-2.2) unstable; urgency=medium
+
+ * Non-maintainer upload.
+ * Fix FTBFS due gcc 10 compilation issues in client/dhclient.c,
+common/discover.c, relay/dhcrelay.c, server/mdb.c, server/mdb6.c
+(closes: 957379).
+
+ -- Leonidas S. Barbosa Wed, 05 Aug 2020 23:08:47 -0300
+
isc-dhcp (4.4.1-2.1) unstable; urgency=medium
* Non-maintainer upload.
diff -Nru isc-dhcp-4.4.1/debian/patches/Fixed_gcc_10_compilation_issues.patch isc-dhcp-4.4.1/debian/patches/Fixed_gcc_10_compilation_issues.patch
--- isc-dhcp-4.4.1/debian/patches/Fixed_gcc_10_compilation_issues.patch 1969-12-31 21:00:00.0 -0300
+++ isc-dhcp-4.4.1/debian/patches/Fixed_gcc_10_compilation_issues.patch 2020-08-05 23:08:34.0 -0300
@@ -0,0 +1,99 @@
+From 129b7e402bd6e7278854e5a8935fce460552b5f4 Mon Sep 17 00:00:00 2001
+From: Thomas Markwalder
+Date: Thu, 30 Jul 2020 10:01:36 -0400
+Subject: [PATCH] [#117] Fixed gcc 10 compilation issues
+
+client/dhclient.c
+relay/dhcrelay.c
+extern'ed local_port,remote_port
+
+common/discover.c
+init local_port,remote_port to 0
+
+server/mdb.c
+extern'ed dhcp_type_host
+
+server/mdb6.c
+create_prefix6() - eliminated memcpy string overflow error
+---
+ RELNOTES | 5 +
+ client/dhclient.c | 5 +++--
+ common/discover.c | 4 ++--
+ relay/dhcrelay.c | 4 ++--
+ server/mdb.c | 2 +-
+ server/mdb6.c | 2 +-
+ 6 files changed, 14 insertions(+), 8 deletions(-)
+
+#diff --git a/RELNOTES b/RELNOTES
+#index 9d0a0414..6919dba7 100644
+#--- a/RELNOTES
+#+++ b/RELNOTES
+#@@ -103,6 +103,11 @@ ISC DHCP is open source software maintained by Internet Systems
+# Consortium. This product includes cryptographic software written
+# by Eric Young (e...@cryptsoft.com).
+#
+#+ Changes since 4.4.2 (Bug Fixes)
+#+
+#+- Minor corrections to allow compilation under gcc 10.
+#+ [Gitlab #117]
+#+
+# Changes since 4.4.2b1 (Bug Fixes)
+#
+# - Added a clarification on DHCPINFORMs and server authority to
+Index: isc-dhcp-4.4.1/client/dhclient.c
+===
+--- isc-dhcp-4.4.1.orig/client/dhclient.c
isc-dhcp-4.4.1/client/dhclient.c
+@@ -81,8 +81,9 @@ static const char message [] = "Internet
+ static const char url [] = "For info, please visit https://www.isc.org/software/dhcp/;;
+ #endif /* UNIT_TEST */
+
+-u_int16_t local_port = 0;
+-u_int16_t remote_port = 0;
++extern u_int16_t local_port;
++extern u_int16_t remote_port;
++
+ #if defined(DHCPv6) && defined(DHCP4o6)
+ int dhcp4o6_state = -1; /* -1 = stopped, 0 = polling, 1 = started */
+ #endif
+Index: isc-dhcp-4.4.1/relay/dhcrelay.c
+===
+--- isc-dhcp-4.4.1.orig/relay/dhcrelay.c
isc-dhcp-4.4.1/relay/dhcrelay.c
+@@ -95,8 +95,8 @@ enum { forward_and_append, /* Forward an
+forward_untouched, /* Forward without changes. */
+discard } agent_relay_mode = forward_and_replace;
+
+-u_int16_t local_port;
+-u_int16_t remote_port;
++extern u_int16_t local_port;
++extern u_int16_t remote_port;
+
+ /* Relay agent server list. */
+ struct server_list {
+Index: isc-dhcp-4.4.1/server/mdb.c
+===
+--- isc-dhcp-4.4.1.orig/server/mdb.c
isc-dhcp-4.4.1/server/mdb.c
+@@ -67,7 +67,7 @@ static host_id_info_t *host_id_info = NU
+
+ int numclasseswritten;
+
+-omapi_object_type_t *dhcp_type_host;
++extern omapi_object_type_t *dhcp_type_host;
+
+ isc_result_t enter_class(cd, dynamicp, commit)
+ struct class *cd;
+Index: isc-dhcp-4.4.1/server/mdb6.c
+===
+--- isc-dhcp-4.4.1.orig/server/mdb6.c
isc-dhcp-4.4.1/server/mdb6.c
+@@ -1943,7 +1943,7 @@ create_prefix6(struct ipv6_pool *pool, s
+ }
+ new_ds.data = new_ds.buffer->data;
+ memcpy(new_ds.buffer->data, ds.data, ds.len);
+- memcpy(new_ds.buffer->data + ds.len, , sizeof(tmp));
++ memcpy(_ds.buffer->data[0] + ds.len, , sizeof(tmp));
+ data_string_forget(, MDL);
+ data_string_copy(, _ds, MDL);
+ data_string_forget(_ds, MDL);
diff -Nru isc-dhcp-4.4.1/debian/patches/series isc-dhcp-4.4.1/debian/patches/series
--- isc-dhcp-4.4.1/debian/patches/series 2020-01-22 18:35:14.0 -0300
+++ isc-dhcp-4.4.1/debian/patches/series 2020-08-05 23:08:47.0 -0300
@@ -16,3 +16,4 @@
bind-includes.patch
configure.patch
+Fixed_gcc_10_compilation_issues.patch
signature.asc
Description: This is a digitally signed message part
