Add and use constants for the Android API levels.

Test: bionic tests still pass
Change-Id: If1b619cfc9db1d3f5d91f14f2ace71058dca0c4a
diff --git a/libc/include/android/legacy_stdlib_inlines.h b/libc/include/android/legacy_stdlib_inlines.h
index 93554e5..e211de5 100644
--- a/libc/include/android/legacy_stdlib_inlines.h
+++ b/libc/include/android/legacy_stdlib_inlines.h
@@ -32,7 +32,7 @@
 #include <stdlib.h>
 #include <sys/cdefs.h>
 
-#if __ANDROID_API__ < 21
+#if __ANDROID_API__ < __ANDROID_API_L__
 
 __BEGIN_DECLS