casts: add casts for unsigned -> signed int

Add WASI support in Abc_Clock

When compiling on Darwin ARM64 hardware using the Conda clang compiler,
compilation fails due to these casts going from `unsigned` to `int`.

In these cases, a cast appears to be the correct approach. Add a cast
to make the compiler happy.

Signed-off-by: Sean Cross <sean@xobs.io>

Add WASI support in Exa4_ManSolve

fix compile warnings

fix compile errors and warnings

Import ttopt

Running SAT-based CEX minimization with multiple POs runs into an
assertion. This makes it produce an error message instead.

Invoking 'constr -r' converts constraints into POs but does not fully
remove them. Now 'constr -pr' can be used to completely remove them,
leaving the set of non-constraint POs unchanged.