Add android_dlwarning() method

This is temporary method intended to use
for a toast message on preview and beta
releases. Will be removed before the
production release.

Bug: http://b/27365747
Change-Id: I39cc716bb82863ae761b6821bcec77cce6db3781
diff --git a/libc/include/android/dlext.h b/libc/include/android/dlext.h
index d5ec386..76d19ae 100644
--- a/libc/include/android/dlext.h
+++ b/libc/include/android/dlext.h
@@ -194,6 +194,8 @@
                                                             uint64_t type,
                                                             const char* permitted_when_isolated_path);
 
+const char* android_dlwarning();
+
 __END_DECLS
 
 #endif /* __ANDROID_DLEXT_H__ */