[fc-arch] Rename architecture names to better reflect what they are

We only care about three properties in the arch:

  - endianness
  - pointer size
  - for 32-bit archs, whether double is aligned on 4 or 8 bytes

This leads to the following 6 archs (old name -> new name):

	x86    -> le32d4
	mipsel -> le32d8
	x86-64 -> le64
	m68k   -> be32d4
	ppc    -> be32d8
	ppc64  -> be64