gnu: isc-dhcp: Adjust for GCC 10.

* gnu/packages/patches/isc-dhcp-gcc-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/admin.scm (isc-dhcp)[source](patches): New field.

gnu/local.mk

@@ -1253,6 +1253,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/iputils-libcap-compat.patch		\
   %D%/packages/patches/ipxe-reproducible-geniso.patch	        \
   %D%/packages/patches/irrlicht-use-system-libs.patch		\
+  %D%/packages/patches/isc-dhcp-gcc-compat.patch		\
   %D%/packages/patches/isl-0.11.1-aarch64-support.patch	\
   %D%/packages/patches/json-c-CVE-2020-12762.patch		\
   %D%/packages/patches/json-c-0.13-CVE-2020-12762.patch	\

gnu/packages/admin.scm

@@ -1152,6 +1152,7 @@ connection alive.")
                 (method url-fetch)
                 (uri (string-append "https://ftp.isc.org/isc/dhcp/"
                                     version "/dhcp-" version ".tar.gz"))
+                (patches (search-patches "isc-dhcp-gcc-compat.patch"))
                 (sha256
                  (base32
                   "06jsr0cg5rsmyibshrpcb9za0qgwvqccashdma7mlm1rflrh8pmh"))))

gnu/packages/patches/isc-dhcp-gcc-compat.patch

@@ -0,0 +1,72 @@
+Add minor fixes for compiling with GCC 10.
+
+Taken from upstream:
+https://gitlab.isc.org/isc-projects/dhcp/-/commit/6c7e61578b1b449272dbb40dd8b98d03dad8a57a
+
+diff --git a/client/dhclient.c b/client/dhclient.c
+--- a/client/dhclient.c
++++ b/client/dhclient.c
+@@ -83,8 +83,9 @@ static const char message [] = "Internet Systems Consortium DHCP Client";
+ 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
+diff --git a/common/discover.c b/common/discover.c
+--- a/common/discover.c
++++ b/common/discover.c
+@@ -45,8 +45,8 @@ struct interface_info *fallback_interface = 0;
+ 
+ int interfaces_invalidated;
+ int quiet_interface_discovery;
+-u_int16_t local_port;
+-u_int16_t remote_port;
++u_int16_t local_port = 0;
++u_int16_t remote_port = 0;
+ u_int16_t relay_port = 0;
+ int dhcpv4_over_dhcpv6 = 0;
+ int (*dhcp_interface_setup_hook) (struct interface_info *, struct iaddr *);
+diff --git a/relay/dhcrelay.c b/relay/dhcrelay.c
+--- a/relay/dhcrelay.c
++++ b/relay/dhcrelay.c
+@@ -95,8 +95,8 @@ enum { forward_and_append,	/* Forward and append our own relay option. */
+        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 {
+diff --git a/server/mdb.c b/server/mdb.c
+--- a/server/mdb.c
++++ b/server/mdb.c
+@@ -67,7 +67,7 @@ static host_id_info_t *host_id_info = NULL;
+ 
+ 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;
+diff --git a/server/mdb6.c b/server/mdb6.c
+--- a/server/mdb6.c
++++ b/server/mdb6.c
+@@ -1945,7 +1945,7 @@ create_prefix6(struct ipv6_pool *pool, struct iasubopt **pref,
+ 		}
+ 		new_ds.data = new_ds.buffer->data;
+ 		memcpy(new_ds.buffer->data, ds.data, ds.len);
+-		memcpy(new_ds.buffer->data + ds.len, &tmp, sizeof(tmp));
++		memcpy(&new_ds.buffer->data[0] + ds.len, &tmp, sizeof(tmp));
+ 		data_string_forget(&ds, MDL);
+ 		data_string_copy(&ds, &new_ds, MDL);
+ 		data_string_forget(&new_ds, MDL);