abuild-sign: fall back to libressl if openssl is missing

openssl binary may be missing while migrating system from libressl to
openssl. Make sure we can always sign the backage if either is there.

abuild-sign.in

@@ -17,6 +17,7 @@ fi
 
 do_sign() {
 	local f i keyname repo
+	local openssl=$(command -v openssl || echo libressl)
 
 	# we are actually only interested in the name, not the file itself
 	keyname=${pubkey##*/}
@@ -29,7 +30,7 @@ do_sign() {
 		set -e
 		cd "$repo"
 		sig=".SIGN.RSA.$keyname"
-		openssl dgst -sha1 -sign "$privkey" -out "$sig" "$i"
+		$openssl dgst -sha1 -sign "$privkey" -out "$sig" "$i"
 		tmptargz=$(mktemp)
 		tar -f - -c "$sig" | abuild-tar --cut | gzip -9 > "$tmptargz"
 		tmpsigned=$(mktemp)