Nullability check for modules in include/android directory

Bugs: b/245972273
Test: adb shell
Change-Id: Ic00d207331d9837a01cf96ec7fe623961e653051
diff --git a/libc/include/android/set_abort_message.h b/libc/include/android/set_abort_message.h
index 5d8d8ee..2be01a9 100644
--- a/libc/include/android/set_abort_message.h
+++ b/libc/include/android/set_abort_message.h
@@ -46,6 +46,6 @@
  *
  * Available since API level 21.
  */
-void android_set_abort_message(const char* __msg) __INTRODUCED_IN(21);
+void android_set_abort_message(const char* _Nullable __msg) __INTRODUCED_IN(21);
 
 __END_DECLS