IVGCVSW-7202 Add Android NDK build targets to build-tool

* Changed build tool scripts to also target Android OS
* Updated Dockerfile to Ubuntu 20.04

Signed-off-by: John Mcloughlin <john.mcloughlin@arm.com>
Change-Id: I6905c205d8870e1628e4885743d9131cb1f11276
diff --git a/build-tool/scripts/validation.sh b/build-tool/scripts/validation.sh
index 48b2372..1d7af76 100755
--- a/build-tool/scripts/validation.sh
+++ b/build-tool/scripts/validation.sh
@@ -1,6 +1,6 @@
 #!/bin/bash
 #
-# Copyright © 2022 Arm Ltd and Contributors. All rights reserved.
+# Copyright © 2022-2023 Arm Ltd and Contributors. All rights reserved.
 # SPDX-License-Identifier: MIT
 #
 
@@ -20,8 +20,8 @@
   exit 1
 fi
 
-if [ "$target_arch" != "aarch64" ] && [ "$target_arch" != "x86_64" ]; then
-  echo "$name: --target-arch is not valid. Valid options are: aarch64, x86_64"
+if [ "$target_arch" != "aarch64" ] && [ "$target_arch" != "android64" ] && [ "$target_arch" != "x86_64" ]; then
+  echo "$name: --target-arch is not valid. Valid options are: aarch64, android64, x86_64"
   exit 1
 fi
 
@@ -32,6 +32,13 @@
   fi
 fi
 
+if [ "$target_arch" == "android64" ]; then
+  if [ "$HOST_ARCH" != "x86_64" ]; then
+    echo "$name: --target_arch android64 is only supported when host is x86_64"
+    exit 1
+  fi
+fi
+
 # Validation of chosen Arm NN dependencies
 if [ "$flag_tflite_classic_delegate" -eq 0 ] && [ "$flag_tflite_opaque_delegate" -eq 0 ] && [ "$flag_tflite_parser" -eq 0 ] && [ "$flag_onnx_parser" -eq 0 ]; then
   echo "$name: at least one of flags --tflite-classic-delegate, --tflite-opaque-delegate, --tflite-parser or --onnx-parser must be set (or --all)."