pagealign_alloc: Add benchmark for comparing different implementations. * lib/pagealign_alloc.h (pagealign_impl_t): New type. (pagealign_impl): New declaration. * lib/pagealign_alloc.c: On native Windows, include <malloc.h> and <windows.h>. (pagealign_impl): New variable. (info_t): Change to a union type. (get_default_impl): New function. (pagealign_alloc, pagealign_free): Dispatch according to pagealign_impl. * tests/bench-pagealign_alloc.c: New file. * modules/pagealign_alloc-tests: New file.