MuPDF does some locking around its allocation calls; it overrides openjpeg's
allocators to do this locking too. However mupdf tries to manually align things
in a way that doesn't match what openjpeg does, which we noticed when frees
were segfaulting because the addresses didn't match up.
In the case of the openjpeg port it's relying on malloc(3)'s guarantee
"The allocated space is suitably aligned (after possible pointer coercion)
for storage of any type of object" so patch mupdf to do the same.