Nearly all structs derived from amd64_attr_t has a size member anyway.
Simplify the code and move it to the base amd64_attr_t.

iropt: Implement 'computed_value_Proj_Builtin' for 'ir_bk_clz', 'ir_bk_ctz', 'ir_bk_ffs', 'ir_bk_parity' and 'ir_bk_popcount'.

Either the conv is used as the new result or it has further users.
In either case it is used afterwards and cannot be removed.

The mode of both nodes is the mode for the GP register class already.

'match_immediate_32()' in the meantime got a parameter 'must_match_ip_relative'.

The documented variable was removed in 2011.

This meant initializing the address mode variant all over the ia32
backend, on the other hand this will be useful if we ever switch the
ia32 backend to a style without NoReg nodes (like amd64).

We only use the immediate and scale yet on ia32.

After a SubSP the top end of the stack is used and not just unused
alignment padding anymore.

Only the backends know how memperm are implementd and whether they use
sp- or fp-relative addressing. This should fix sparc memperm problems.

Long-term I'd like to remove the memperm node and use a callback that
creates a sequence of target specific nodes instead (similar to how
spills and reloads are created).

This is a bigger rewrite of stack frame handling in the backend:

- Do the stack frame type layout late, after all the spill slots have
  been created. This way we can avoid (and remove) the brittle
  frame_alloc_area().
- Standardize the meaning of stack entity offsets. After stack frame type
  layout they are relative to the stack pointer position at the beginning
  of the function.  It is all in one type now, no splitting into "arg",
  "between" and "stack_frame" type anymore.
- Generalize the stack pointer simulation code to work with a single
  callback. Represent stack state as current offset and align_padding
  number. Now that callbacks can access and modify them both we do not
  need custom code in the sparc backend anymore.
- Remove alignment specification on IncSP, only keep a ignore_align flag
  used for the last IncSP that has to remove all existing sp adjustments
  and may end up on a misaligned SP on ia32/amd64.
- Align stack by default on ia32+amd64 backends.

They are not used yet as we need an adapted layout algorithm for them.