Implement CA - ternary short circuit for constant T/F expressions.
Implement CA - ternary short circuit for constant T/F expressions.

This patch only applies to the ternary operator when used in a
continuous assignment. It adds short circuiting when the expression
is a constant true or false. It does not optimize the special case of
a constant 'bx expression with constant T/F expressions.

CastMi/iverilog,CastMi/iverilog,CastMi/iverilog,themperek/iverilog,themperek/iverilog,themperek/iverilog