Always generate code for .selector member access.

test/libsolidity/semanticTests/functionTypes/selector_expression_side_effect.sol

@@ -0,0 +1,13 @@
+contract C {
+	uint x;
+	function f() public returns (uint256) {
+		h().f.selector;
+		return x;
+	}
+	function h() public returns (C) {
+		x = 42;
+		return this;
+	}
+}
+// ----
+// f() -> 42