Fix compilation error in ia64-tdep.c with libunwind-ia64

Commit

  9018be22e022 ("Make target_read_alloc & al return vectors")

failed to update the code in ia64-tdep.c, for HAVE_LIBUNWIND_IA64_H.
This patch fixes that.

gdb/ChangeLog:

	* ia64-tdep.c (ktab_buf): New global.
	(getunwind_table): Return a gdb::optional<gdb::byte_vector>.
	(get_kernel_table): Adjust.
1 file changed