Since the commpage is at a kernel address, changed 64-bit paging code
to match x86's behaviour of allowing user-accessible mappings to be
created in the kernel portion of the address space. This is also
required by some drivers.
* x86_64 is using the existing *_ia32 boot platforms.
* Special flags are required when compiling the loader to get GCC to compile
32-bit code. This adds a new set of rules for compiling boot code rather
than using the kernel rules, which compile using the necessary flags.
* Some x86_64 private headers have been stubbed by #include'ing the x86
versions. These will be replaced later.
