Add Linux/ia64 core file note support to BFD.

The generic elfcore_grok_prstatus() in bfd/elf.c only recognises a
NT_PRSTATUS note whose size matches the *host* prstatus_t. On any host
other than ia64 the 1144 byte Linux/ia64 note is therefore skipped, no
.reg pseudo section is created and GDB fails with

  warning: Couldn't find general-purpose registers in core file.

which makes ia64 core files unreadable with a cross GDB. Provide the
ia64 elf_backend_grok_prstatus / elf_backend_grok_psinfo hooks with the
Linux/ia64 offsets so cross debugging works.

Signed-off-by: René Rebe <rene@exactco.de>

--- gdb-17.2/bfd/elfnn-ia64.c
+++ gdb-17.2/bfd/elfnn-ia64.c
@@ -1,5 +1,6 @@
 /* IA-64 support for 64-bit ELF
    Copyright (C) 1998-2025 Free Software Foundation, Inc.
+   Copyright (C) 2026 René Rebe <rene@exactco.de>
    Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
 
    This file is part of BFD, the Binary File Descriptor library.
@@ -4984,6 +4985,68 @@ static void
 ignore_errors (const char *fmt ATTRIBUTE_UNUSED, ...)
 {
 }
+
+/* Linux/ia64 core file support.  Without these the generic code in elf.c
+   only groks a NT_PRSTATUS whose size matches the *host* prstatus_t, so
+   no .reg section is created when an ia64 core is read on any other host
+   and the register state is unavailable.  */
+
+static bool
+elfNN_ia64_grok_prstatus (bfd *abfd, Elf_Internal_Note *note)
+{
+  int offset;
+  size_t size;
+
+  switch (note->descsz)
+    {
+    default:
+      return false;
+
+    case 1144:			/* Linux/ia64 */
+      /* pr_cursig */
+      elf_tdata (abfd)->core->signal = bfd_get_16 (abfd, note->descdata + 12);
+
+      /* pr_pid */
+      elf_tdata (abfd)->core->lwpid = bfd_get_32 (abfd, note->descdata + 32);
+
+      /* pr_reg */
+      offset = 112;
+      size = 1024;		/* ELF_NGREG * sizeof (elf_greg_t) */
+      break;
+    }
+
+  return _bfd_elfcore_make_pseudosection (abfd, ".reg", size,
+					  note->descpos + offset);
+}
+
+static bool
+elfNN_ia64_grok_psinfo (bfd *abfd, Elf_Internal_Note *note)
+{
+  char *command;
+  int n;
+
+  switch (note->descsz)
+    {
+    default:
+      return false;
+
+    case 136:			/* Linux/ia64 elf_prpsinfo */
+      elf_tdata (abfd)->core->pid = bfd_get_32 (abfd, note->descdata + 24);
+      elf_tdata (abfd)->core->program
+	= _bfd_elfcore_strndup (abfd, note->descdata + 40, 16);
+      elf_tdata (abfd)->core->command
+	= _bfd_elfcore_strndup (abfd, note->descdata + 56, 80);
+      break;
+    }
+
+  /* Strip the spurious trailing space some implementations append.  */
+  command = elf_tdata (abfd)->core->command;
+  n = strlen (command);
+  if (n > 0 && command[n - 1] == ' ')
+    command[n - 1] = '\0';
+
+  return true;
+}
 
 #define TARGET_LITTLE_SYM		ia64_elfNN_le_vec
 #define TARGET_LITTLE_NAME		"elfNN-ia64-little"
@@ -5075,6 +5138,8 @@ ignore_errors (const char *fmt ATTRIBUTE
 #define elf_backend_dtrel_excludes_plt	1
 #define elf_backend_special_sections	elfNN_ia64_special_sections
 #define elf_backend_default_execstack	0
+#define elf_backend_grok_prstatus	elfNN_ia64_grok_prstatus
+#define elf_backend_grok_psinfo		elfNN_ia64_grok_psinfo
 
 /* FIXME: PR 290: The Intel C compiler generates SHT_IA_64_UNWIND with
    SHF_LINK_ORDER. But it doesn't set the sh_link or sh_info fields.