Patch by Robert Scheck <robert@fedoraproject.org> for iftop <= 1.0pre4 to avoid a
GCC 10 related build failure due to global variables in a header file with omitted
"extern" declaration, see also: https://gcc.gnu.org/gcc-10/porting_to.html

Example build failure output:
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: multiple definition of `screen_list'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaktotal'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peakrecv'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaksent'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: multiple definition of `totals'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: multiple definition of `screen_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: first defined here
/usr/bin/ld: ui_common.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: multiple definition of `service_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: multiple definition of `screen_list'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaksent'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peakrecv'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaktotal'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: multiple definition of `totals'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: multiple definition of `screen_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: first defined here
/usr/bin/ld: ui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: multiple definition of `service_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: multiple definition of `screen_list'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:36: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: multiple definition of `totals'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:37: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaksent'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peakrecv'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: multiple definition of `peaktotal'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:38: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: multiple definition of `screen_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:40: first defined here
/usr/bin/ld: tui.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: multiple definition of `service_hash'; iftop.o:/builddir/build/BUILD/iftop-1.0pre4/ui_common.h:41: first defined here
collect2: error: ld returned 1 exit status

--- iftop-1.0pre4/ui_common.h			2020-02-02 23:58:40.104880963 +0100
+++ iftop-1.0pre4/ui_common.h.gcc10		2020-02-02 23:59:36.822197955 +0100
@@ -33,12 +33,12 @@
 
 extern options_t options;
 
-sorted_list_type screen_list;
-host_pair_line totals;
-int peaksent, peakrecv, peaktotal;
+extern sorted_list_type screen_list;
+extern host_pair_line totals;
+extern int peaksent, peakrecv, peaktotal;
 extern history_type history_totals;
-hash_type* screen_hash;
-hash_type* service_hash;
+extern hash_type* screen_hash;
+extern hash_type* service_hash;
 
 void analyse_data(void);
 void screen_list_init(void);
--- iftop-1.0pre4/ui_common.c			2020-02-02 23:58:40.104880963 +0100
+++ iftop-1.0pre4/ui_common.c.gcc10		2020-02-03 00:06:14.604323838 +0100
@@ -27,6 +27,12 @@
   [OPTION_BW_PKTS]  = { "p", "Kp", "Mp", "GB"},
 };
 
+sorted_list_type screen_list;
+host_pair_line totals;
+int peaksent, peakrecv, peaktotal;
+hash_type* screen_hash;
+hash_type* service_hash;
+
 extern hash_type* history;
 extern int history_pos;
 extern int history_len;