Vsyscall hook rearrangement

This patch series tidies up the vsyscall hook bits in a similar fashion to the traced syscall bits.  The big change is moving out assembly functions to their own files.  The other two changes are just small refinements.

After this, one *ought* to be able to compile the library in PIC mode, but several failures still show up locally when I do that.  I haven't traced them down to VMWare emulation issues or actual PIC bugs, though I am suspecting the former.