This fixes opt/fehler261.c.

For details see endless loops section on the homepage.

The semantics on when to set this flag were unclear, so there weren't
any real users anyway.

- Mux((a & 1) != 0, 0, b) => -a & b
- Mux((a & 1) == 0, 0, b) => (a - 1) & b

This should fix x86code/funcana_nowrite2.c

This should fix strange overly long immediate values emitted in the
assembler sometimes.

We can now differentiate between objects with compound type and
primitive type.

This fixes opt/fehler260.c.

- We have no_write, pure and terminates now (terminates instead of
  has_loop means that more flags is more specific information, so the
  fixpoint algos are less confusing)
- funccall ana also detects noreturn attribute now (but isn't optimizing
  it)

Value live_after() is a special case of the checks performed in
values_interfere(). This commit extracts this code and use the new function
where possible.