Add macro hygiene test

Author: Sa4dUs

tests/codegen-llvm/autodiff/macro_hygiene.rs

@@ -0,0 +1,22 @@
+//@ compile-flags: -Zautodiff=Enable -C opt-level=3  -Clto=fat
+//@ no-prefer-dynamic
+//@ needs-enzyme
+
+// In the past, we just checked for correct macro hygiene information.
+
+#![feature(autodiff)]
+
+// CHECK: ;
+macro_rules! demo {
+    () => {
+        #[std::autodiff::autodiff_reverse(fd, Active, Active)]
+        fn f(x: f64) -> f64 {
+            x * x
+        }
+    };
+}
+demo!();
+
+fn main() {
+    dbg!(f(2.0f64));
+}