From: Jan Engelhardt <jengelh@inai.de>
Date: 2020-09-17 10:32:23.591643664 +0200

It's either gcc -fcommon, or a source patch.

---
 src/mismatches.c |    2 ++
 src/mismatches.h |    2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

Index: conauto-2.03/src/mismatches.c
===================================================================
--- conauto-2.03.orig/src/mismatches.c
+++ conauto-2.03/src/mismatches.c
@@ -23,6 +23,8 @@
 #define TRUE 1
 #define FALSE 0
 
+uint16_t mismatch_found_hash;
+
 void mark_new_mismatch ( Partition *p, uint8_t *mm_marked, Info_Vertex *info_vert, uint16_t mmv )
 {
 	const MismatchCollection *mm = p->mm_collection;
Index: conauto-2.03/src/mismatches.h
===================================================================
--- conauto-2.03.orig/src/mismatches.h
+++ conauto-2.03/src/mismatches.h
@@ -22,7 +22,7 @@
 #include <stdlib.h>
 #include <inttypes.h>
 
-uint16_t mismatch_found_hash;
+extern uint16_t mismatch_found_hash;
 
 typedef struct {
 	uint16_t *mismatch_hash;