The function also returns true for zero even though that is not a power
of two.

computed_value() uses some non-trivial patterns (Confirm nodes etc.)
that break the assumption that the transfer function only looks at its
direct operands.

This fixes opt/fehler313.c.

set_irn_link checks whether the resource is allocated.

Only keep the basics necessary to emit text lines in beemitter.[ch] and
move all the other convenience stuff to beemithlp.[ch].

We previously left the amd64_addr_t attribute uninitialized for OP_REG,
OP_REG_REG and OP_REG_IMM. Make the code more consistent by always
initializing it to the newly introduced X86_ADDR_REG variant, as a bonus
we can also use base_input member to indicate the register input instead
of hardcoding it to 0.