The tarval module is not the place to validate your input, leave that to
frontends and others... This way the code is simpler and slightly
faster.

Most inputs are little endian anyway and the few remaining users can
easily swap the bytes themselfes instead of having the function swap
them.

All users construct their Keeps in one go.

In particular create Keeps for mode_T nodes in one go instead of adding one Proj to the Keep after another.

The missing keeps walker does this for us.

new_ir_node() already does, now init_node_attr() does, too.

It was only used in one place, where it is easily replaced.

be_Return is no more.

There is no legitimate reason for an outside user to change the op of a node.
Even internally it should be used less, i.e. only for Deleted, Id and Tuple.

The nodes in question already have this op.
This is some legacy when there were Conv_I2I and Conv_I2I8Bit.

amd64, ia32: Encode the length of the constraint list in the type instead of relying on matching magic numbers.

Remove the unused OVERFLOW_SATURE case and switch the type to a simple
wrap_on_overflow bool.