CMake: Fix Introspection builds

We need to add -DHB_AAT_H and -DHB_AAT_H_IN to the flags that are passed
to g-ir-scanner, so that introspection builds can proceed normally.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2d6e77e..b6241e9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -696,6 +696,8 @@
       -DHB_H_IN
       -DHB_OT_H
       -DHB_OT_H_IN
+      -DHB_AAT_H
+      -DHB_AAT_H_IN
       -DHB_GOBJECT_H
       -DHB_GOBJECT_H_IN
       -DHB_EXTERN=