[PATCH] [gdb] Fix assert in delete_breakpoint

[Tom de Vries <tdevries@suse.de>]

On a pinebook (aarch64 with 64-bit kernel and 32-bit userland) with test-case
gdb.base/gdb-sigterm.exp I run into:
...
intrusive_list.h:458: internal-error: erase_element: \
  Assertion `elem_node->prev != INTRUSIVE_LIST_UNLINKED_VALUE' failed.^M
...

Fix this similar to:
- commit c0afd99439f ("[gdb/tui] Fix assert in ~gdbpy_tui_window_maker"), and
- commit 995a34b1772 ("Guard against frame.c destructors running before
  frame-info.c's"
by checking is_linked () before attempting to remove from breakpoint_chain.

Tested on the pinebook and x86_64-linux.

PR gdb/31061
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31061
---
 gdb/breakpoint.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index fe09dbcbeee..0a58821fc00 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -12633,7 +12633,8 @@ delete_breakpoint (struct breakpoint *bpt)
   if (bpt->number)
     notify_breakpoint_deleted (bpt);
 
-  breakpoint_chain.erase (breakpoint_chain.iterator_to (*bpt));
+  if (bpt->is_linked ())
+    breakpoint_chain.erase (breakpoint_chain.iterator_to (*bpt));
 
   /* Be sure no bpstat's are pointing at the breakpoint after it's
      been freed.  */

base-commit: 6b682bbf86f37982ce1d270fb47f363413490bda
-- 
2.35.3