Add Android U API level to NDK headers

Test: Build
Change-Id: Ic1e0d8b7e5abf07045944d2f610764709b45c923
diff --git a/libc/include/android/api-level.h b/libc/include/android/api-level.h
index ecf318d..650bb95 100644
--- a/libc/include/android/api-level.h
+++ b/libc/include/android/api-level.h
@@ -154,6 +154,9 @@
 /** Names the "T" API level (33), for comparison against `__ANDROID_API__`. */
 #define __ANDROID_API_T__ 33
 
+/** Names the "U" API level (34), for comparison against `__ANDROID_API__`. */
+#define __ANDROID_API_U__ 34
+
 /* This file is included in <features.h>, and might be used from .S files. */
 #if !defined(__ASSEMBLY__)