[SMTChecker] Supporting conditional operator

test/libsolidity/smtCheckerTests/operators/conditional_assignment_6.sol

@@ -0,0 +1,26 @@
+pragma experimental SMTChecker;
+
+abstract contract D {
+    function d() public virtual ;
+}
+
+contract C {
+    bool a;
+    uint x;
+    D d;
+    function g() public returns (uint) {
+        x = 2;
+        d.d();
+        return x;
+    }
+    function f(bool b) public {
+        x = 1;
+        uint y = b ? g() : 3;
+        assert(x == 2 || x == 1);
+    }
+    function h() internal {
+        x = 3;
+    }
+}
+// ----
+// Warning 2072: (288-294): Unused local variable.