Fix for -fno-common

Index: setversion
--- setversion.orig
+++ setversion
@@ -24,7 +24,7 @@ vsh='src/version.h'
 echo -n '' > $vsh
 echo '#ifndef zoem_version_h__' >> $vsh
 echo '#define zoem_version_h__' >> $vsh
-echo 'char *zoemDateTag;' >> $vsh
+echo 'extern char *zoemDateTag;' >> $vsh
 echo '#endif' >> $vsh
 
 vsc='src/version.c'