For stabs debug info it was used to suppress debug info, so set ir_visibility_private instead.

Avoid using the op_pin_state enum as that contains confusing additional
entries that are not valid on a node. The only remaining state for a
node is pinned/floating which we can simply represent with a 0/1 value.

This adds two builtin kinds, ir_bk_va_start and ir_bk_va_arg. va_arg Builtins
are lowered in the lower_builtins pass with a function provided by the backend,
whereby most architectures can use be_default_lower_va_args. va_start Builtins
are lowered in the backend.

Note: This commit breaks all backends except for IA32. SPARC and AMD64 are
implemented in later commits. The ARM backend previously miscompiled variadic
functions, and will now throw a proper error.

The next release will feature a cmake build.

There is no node left that uses it.

This reverts commit 5165321c.

lower_highlevel() is used by x10i.
Also, I'd argue we should rather deprecate lower_highlevel_graph
instead.

Both functions do the same and the former is used way less.

This reverts commit 7efc2374.

The function was used by the compiler lab reference compiler.

See 364d7fce for details.

Also provide a cleaner, better documented and slightly faster
implementation.

- block_strictly_dominates() is trivially to compute yourself anyway.
- free_dom() and free_postdom() did not free any memory anyway and the
  irg_properties handling is performed by confirm_irg_properties()
  anyway.

We only use control flow scc analysis.