Stop using the __ANDROID_API_x__ constants.

Historically we've made a few mistakes where they haven't matched the
right number. And most non-Googlers are much more familiar with the
numbers, so it seems to make sense to rely more on them. Especially in
header files, which we actually expect real people to have to read from
time to time.

Test: treehugger
Change-Id: I0d4a97454ee108de1d32f21df285315c5488d886
diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index c45c91f..23a58d6 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -66,7 +66,7 @@
 /** Flag for open(). */
 #define O_RSYNC O_SYNC
 
-#if __ANDROID_API__ >= __ANDROID_API_L__
+#if __ANDROID_API__ >= 21
 /** Flag for splice(). */
 #define SPLICE_F_MOVE 1
 /** Flag for splice(). */
@@ -77,7 +77,7 @@
 #define SPLICE_F_GIFT 8
 #endif
 
-#if __ANDROID_API__ >= __ANDROID_API_O__
+#if __ANDROID_API__ >= 26
 /** Flag for sync_file_range(). */
 #define SYNC_FILE_RANGE_WAIT_BEFORE 1
 /** Flag for sync_file_range(). */