[llvm] Mark test as XFAIL that started failing after 418f006. (PR #85027)

[via llvm-commits]

https://github.com/dyung created https://github.com/llvm/llvm-project/pull/85027

Similar failures were previously seen and XFAILed in https://reviews.llvm.org/D118468.

See the phabricator review for a description of the problem, and the linked discourse thread for what the failing output looks like.

This change should fix the issue on two buildbots that are running older versions of GDB:
- https://lab.llvm.org/buildbot/#/builders/217/builds/37559
- https://lab.llvm.org/buildbot/#/builders/247/builds/15173

>From 273dc962c520f9f5398a96de92ec0f4a70030186 Mon Sep 17 00:00:00 2001
From: Douglas Yung <dyung+github at fastmail.fm>
Date: Tue, 12 Mar 2024 23:43:07 -0700
Subject: [PATCH] Mark test as XFAIL that started failing after 418f006.

Similar failures were previously seen and XFAILed in https://reviews.llvm.org/D118468.
---
 .../debuginfo-tests/llgdb-tests/forward-declare-class.cpp        | 1 +
 1 file changed, 1 insertion(+)

diff --git a/cross-project-tests/debuginfo-tests/llgdb-tests/forward-declare-class.cpp b/cross-project-tests/debuginfo-tests/llgdb-tests/forward-declare-class.cpp
index 850eed6ad95d98..130c439faec8cd 100644
--- a/cross-project-tests/debuginfo-tests/llgdb-tests/forward-declare-class.cpp
+++ b/cross-project-tests/debuginfo-tests/llgdb-tests/forward-declare-class.cpp
@@ -1,6 +1,7 @@
 // RUN: %clangxx %target_itanium_abi_host_triple -O0 -g %s -c -o %t.o
 // RUN: %test_debuginfo %s %t.o
 // Radar 9168773
+// XFAIL: !system-darwin && gdb-clang-incompatibility
 
 // DEBUGGER: ptype A
 // Work around a gdb bug where it believes that a class is a