GitLab

- alignment is set on each single IncSP now instead of a global arch_env
  setting
- fixed ia32 not requesting any alignment anymore (even on darwin where
  we need it)
- fixed amd64 creating IncSP nodes without flag_modifies_flags set

This removes functions from the public API which are pointless outside
localopt rules, and also avoids another struct in the public API.

The start block is not special block without any "real" instructions
anymore. In particular this means:

- There is no X_initial_exec Proj from the Start node anymore, "normal"
  cfopts are used for jumping out of the start block.
- The backend never had the special convention of the start block not
  containing actual code and used to fixup this discrpancy, no more
  fixup code needed now.
- The part_block() code got a bit more complicated because splitting the
  start block is tricky (previously part_block() simply failed in this
  case but was never used in the Start block because of its special
  convention)

- It was only available in the ia32 backend and broken there. As the
  feature is rarely used, I remove it for now instead of going through
  the trouble of fixing it.

Implemented for now: When the flags of one Sub or Cmp node are needed, but
the flags of another one are currently alive, invert the condition code and
avoid rematerialization.

- We now create a spill/reload/phi-web and take the largest necessary
  reload size to determine the size of the entities and the spills.
- Some cleanups

This also disables the memcombine optimisation if unaligned stores are
not supported by the backend.
We may add some tests in the future to reenable this in cases where we
can prove that the combined store is aligned.