[SMTChecker] Added support for selector when expression's value is known at compile time

test/libsolidity/smtCheckerTests/function_selector/selector.sol

@@ -0,0 +1,8 @@
+pragma experimental SMTChecker;
+
+contract C {
+    function f() public pure {
+        assert(msg.sig == this.f.selector);
+    }
+}
+// ----