Make android_get_application_target_sdk_version available to the NDK.

Also move this and android_get_device_api_level into <android/api-level.h>
so that they're always available.

This involves cleaning up <sys/cdefs.h> slightly.

Bug: N/A
Test: builds
Change-Id: I25435c55f3549cd0d827a7581bee75ea8228028b
diff --git a/tests/android_get_device_api_level.cpp b/tests/android_get_device_api_level.cpp
index 5272a48..0662404 100644
--- a/tests/android_get_device_api_level.cpp
+++ b/tests/android_get_device_api_level.cpp
@@ -29,7 +29,7 @@
 #include <gtest/gtest.h>
 
 #if __BIONIC__
-#include <android/get_device_api_level.h>
+#include <android/api-level.h>
 #endif
 
 TEST(android_get_device_api_level, smoke) {
diff --git a/tests/libdl_test.cpp b/tests/libdl_test.cpp
index 0c2bf67..6774f1d 100644
--- a/tests/libdl_test.cpp
+++ b/tests/libdl_test.cpp
@@ -18,7 +18,6 @@
 
 #include <android/api-level.h>
 
-extern "C" int android_get_application_target_sdk_version();
 extern "C" void android_set_application_target_sdk_version(int target);
 
 TEST(libdl, application_sdk_versions_smoke) {