Add Testcases For other Fixed issues (dlang#21231)

Author: abulgit

compiler/test/fail_compilation/fix21165.d

@@ -1,10 +1,30 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/fix21165.d(9): Error: undefined identifier `foo`
+fail_compilation/fix21165.d(12): Error: undefined identifier `foo`
+fail_compilation/fix21165.d(16): Error: undefined identifier `foo`
+fail_compilation/fix21165.d(21): Error: undefined identifier `foo`
+fail_compilation/fix21165.d(30): Error: undefined identifier `foo`
 ---
 */
 
 // Test case from Issue #21165
 foo
 f() {}
+
+// Test case from Issue #21171
+foo
+bar;
+
+// Test case from Issue #21169
+void fun(
+	foo x
+) {}
+
+// Test case from Issue #21168
+enum plusOne(int x) = x + 1;
+
+alias fooPlusOne =
+	plusOne
+	!
+	foo;