Show code that caused unreachable code #2207

`$echo` would suppress warning about unreachable code. #2205

test/test_suite/functions/unreachable_code_trace.c3

@@ -0,0 +1,12 @@
+import std;
+
+macro something() {
+	unreachable("Hi there");
+}
+
+fn void main() {
+	something();
+
+	$echo "Hello";
+	io::printn("Hello, World"); // #warning: This code will never execute
+}