x86_64: fix syscall stubs so that syscall5 properly specifies the fifth parameter.

select() now functions as expected on x86_64; it no longer gets cruft as its timeout parameter (and therefore immediate-return selects work again, which makes curses much happier!).
posix: various logging updates, fix select() to return EINVAL for nfds == 0
vfs: fix iterator logic fail in MemoryMapManager::remove.

It was possible that removing the most-recently-created mmap in its entirety would cause an infinte loop here, this has been resolved.