Indeed; Linux has posix_memalign, and mingw never runs the io helper
(although it does compile it, hence the #if). If gnulib would give
us posix_memalign on mingw, we could nuke this #if altogether.
That's pretty difficult (unless you also add a posix_memalign_free)
because at the time posix_memalign returns you have lost the base
pointer for free().
Paolo