xen/link: Include .debug_str_offsets in DWARF2_DEBUG_SECTIONS

xen/link: Include .debug_str_offsets in DWARF2_DEBUG_SECTIONS

Building Xen with Clang-17 yields the following warning:

  ld: warning: orphan section `.debug_str_offsets' from `prelink.o' being placed in section `.debug_str_offsets'
  ld: ./.xen.efi.0xffff82d040000000.0:/4: section below image base
  ld: ./.xen.efi.0xffff82d040000000.1:/4: section below image base
  ld: warning: orphan section `.debug_str_offsets' from `prelink.o' being placed in section `.debug_str_offsets'
  ld: xen.efi:/4: section below image base

Set the alignment to 4 as it holds 4-byte values, despite the fact that Clang
appears to only use 1.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>