process-debuginfo: Do not call eu-elfcompress if it doesn't exist

E2K arch have old elfutils-0.159 which doesn't have eu-elfcompress.
Error:

  /usr/lib/rpm/process-debuginfo: line 68: eu-elfcompress: command not found

Reported-by: Andrey Savchenko <bircoph@altlinux.org>

scripts/process-debuginfo.in

@@ -64,7 +64,7 @@ if [ -n "$strip" ]; then
 	mkdir -p "${debugf%/*}"
 	LD_ORIGIN_PATH=/usr/bin eu-strip $strip --remove-comment -f "$debugf" "$f"
 
-	if [ -n "$elfcompress" ]; then
+	if [ -n "$elfcompress" ] && [ -x /usr/bin/eu-elfcompress ]; then
 		LD_ORIGIN_PATH=/usr/bin eu-elfcompress --quiet "$debugf"
 	fi