Switch to NDK API level 21

PiperOrigin-RevId: 280766624
Change-Id: I8500b69a5f6bebbeb0aafcf5744f5be5944738b9

configure.py

@@ -818,7 +818,7 @@ def get_ndk_api_level(environ_cp, android_ndk_home_path):
   android_ndk_api_level = prompt_loop_or_load_from_env(
       environ_cp,
       var_name='ANDROID_NDK_API_LEVEL',
-      var_default='18',  # 18 is required for GPU acceleration.
+      var_default='21',  # 21 is required for ARM64 support.
       ask_for_var=('Please specify the (min) Android NDK API level to use. '
                    '[Available levels: %s]') % api_levels,
       check_success=valid_api_level,

tensorflow/lite/g3doc/guide/android.md

@@ -132,7 +132,7 @@ in the `.tf_configure.bazelrc` file in the root folder:
 
 ```shell
 build --action_env ANDROID_NDK_HOME="/usr/local/android/android-ndk-r17c"
-build --action_env ANDROID_NDK_API_LEVEL="18"
+build --action_env ANDROID_NDK_API_LEVEL="21"
 build --action_env ANDROID_BUILD_TOOLS_VERSION="28.0.3"
 build --action_env ANDROID_SDK_API_LEVEL="23"
 build --action_env ANDROID_SDK_HOME="/usr/local/android/android-sdk-linux"

tensorflow/tools/ci_build/Dockerfile.android

@@ -29,7 +29,7 @@ RUN mkdir -p ${ANDROID_DEV_HOME}
 ENV ANDROID_SDK_FILENAME tools_r25.2.5-linux.zip
 ENV ANDROID_SDK_URL https://dl.google.com/android/repository/${ANDROID_SDK_FILENAME}
 ENV ANDROID_API_LEVEL 23
-ENV ANDROID_NDK_API_LEVEL 18
+ENV ANDROID_NDK_API_LEVEL 21
 # Build Tools Version liable to change.
 ENV ANDROID_BUILD_TOOLS_VERSION 28.0.0
 ENV ANDROID_SDK_HOME ${ANDROID_DEV_HOME}/sdk

tensorflow/tools/ci_build/builds/builds_common.sh

@@ -235,7 +235,7 @@ android_sdk_repository(
 android_ndk_repository(
     name="androidndk",
     path="${ANDROID_NDK_HOME}",
-    api_level=18)
+    api_level=21)
 EOF
     fi
   fi