This caused a couple of .o files to change size. I had a look at one,
and it seems to be caused by the difference in size of these two
instructions:
    49 8b 5d 08            mov    0x8(%r13),%rbx
    49 8b 5c 24 08         mov    0x8(%r12),%rbx
(with a few nops being added or removed later in the file, presumably
for alignment reasons).