- Replace limit callback in register requirements with a simple bitset
- Fix backends, generators and the rest of the code for the change register
  requirements structure
- Eliminated the custom register_requirement structures in the backend, they
  are pointless now, use the normal arch_register_req_t
- Fix TEMPLATE backend
- Extract emitter framework from ia32 and provide generic header/code for it
- Port TEMPLATE backend to new emitter
- Extract gas specific emit stuff (declarations, sections) from ia32 backend
  and provide it as generic header/code. Make TEMPLATE backend use that
- Remove several FIRM_DBG_REGISTERs from functions which are called very often.
  Before we had millions of string hashtable lookups because of that. The
  prefered way is to have 1 static debug module per file and initialize it in
  the module constructor. No passing around in environment structs and in no
  case should you dynamically register it in single functions.