Update version to v2.0.0-rc4

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Idfe7be3fc2eb22bf1e526d6fe6aeb0ce0f5aae88
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2397
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>

configure.ac

@@ -29,7 +29,7 @@ AC_PREREQ([2.50])
 m4_define([bt_version_major], [2])
 m4_define([bt_version_minor], [0])
 m4_define([bt_version_patch], [0])
-m4_define([bt_version_extra], [-rc2])
+m4_define([bt_version_extra], [-rc4])
 m4_define([bt_version], bt_version_major[.]bt_version_minor[.]bt_version_patch[]bt_version_extra)
 
 AC_INIT([babeltrace], bt_version, [jeremie dot galarneau at efficios dot com], [], [https://efficios.com/babeltrace/])