Avoid non-C++-enabled babeltrace versions

In some babeltrace versions before 1.2.0, the header file iterator.h
declares the enum values `BT_SEEK_*' within the struct declaration of
bt_iter_pos.  The enum values are supposed to be globally-scoped, which
works for C, but not for C++.  Later babeltrace versions declare the
enum outside the struct:

  https://lists.lttng.org/pipermail/lttng-dev/2013-September/021411.html

Now that GDB is compiled with C++, the GDB build fails on a system with
an affected babeltrace version: the compiler complains about a missing
declaration of BT_SEEK_BEGIN in ctf.c.

This patch enhances the configure check to recognize such babeltrace
versions as unusable for GDB.

gdb/ChangeLog:

	* configure.ac: Enhance configure check for babeltrace to reject
	non-C++-enabled versions.
	* configure: Regenerate.

1 files changed, 1 insertions, 0 deletions

diff --git a/gdb/configure b/gdb/configure
index 3cf95e7..228cb99 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -16390,6 +16390,7 @@ struct bt_iter_pos *pos = bt_iter_get_pos (bt_ctf_get_iter (NULL));
 			struct bt_ctf_event *event = NULL;
 			const struct bt_definition *scope;
 
+			pos.type = BT_SEEK_BEGIN;
 			bt_iter_set_pos (bt_ctf_get_iter (NULL), pos);
 			scope = bt_ctf_get_top_level_scope (event,
 			      				   BT_STREAM_EVENT_HEADER);