* Make a PPC32-specific code emitter because we have separate classes for 32-

  and 64-bit code emitters that cannot share code unless we use virtual
  functions
* Identify components being built by tablegen with more detail by assigning them
  to PowerPC, PPC32, or PPC64 more specifically; also avoids seeing 'building
  PowerPC XYZ' messages twice, where one is for PPC32 and one for PPC64

llvm-svn: 16980