don't use -m flag to grep - it's unavailable in OpenBSD

bld/get-version

@@ -18,7 +18,7 @@ elif grep '\$Format:%d\$' VERSION >/dev/null 2>&1; then
 # unsubstituted VERSION, but no git available.
     echo UNKNOWN
 else
-     vers=`cat VERSION | sed 's/[(), ]/\n/ g' | grep -m 1 $v[0-9]`
+     vers=`cat VERSION | sed 's/[(), ]/\n/ g' | grep $v[0-9] | head -n 1`
 
      if [ $? -eq 0 ]; then
          echo ${vers#v}