A warning about 5.12-rc1

From my reading, they're relevant: the bug is old (2014) but only affected swapfiles on filesystems that are, frankly, quite unlikely to be used to house swapfiles (who on earth would put a swapfile on zmem?!) before a simplification in 2.12-rc made it affect, well, more or less everything. (Not that I can track down the latter change in five minutes of grepping around.)