add warning with install instructions when android build-tools are not found

Change-Id: I987262e4e9ae99c889285658fc9f840655d29191

configure.ac

@@ -848,6 +848,16 @@ if echo "$host_os" | grep -q linux-android ; then
     if test ! -d "$ANDROID_SDK_HOME/platforms"; then
         AC_MSG_ERROR([the --with-android-sdk option does not point to an Android SDK])
     fi
+
+    BUILD_TOOLS_VERSION=`$SED -n -e 's/.*buildToolsVersion "\(.*\)"/\1/p' $SRC_ROOT/android/source/build.gradle`
+    if test ! -d "$ANDROID_SDK_HOME/build-tools/$BUILD_TOOLS_VERSION"; then
+        AC_MSG_WARN([android build-tools $BUILD_TOOLS_VERSION not found - install with
+                         $ANDROID_SDK_HOME/tools/android update sdk -u --all --filter build-tools-$BUILD_TOOLS_VERSION
+                    or adjust change $SRC_ROOT/android/source/build.gradle accordingly])
+        add_warning "android build-tools $BUILD_TOOLS_VERSION not found - install with"
+        add_warning "    $ANDROID_SDK_HOME/tools/android update sdk -u --all --filter build-tools-$BUILD_TOOLS_VERSION"
+        add_warning "or adjust $SRC_ROOT/android/source/build.gradle accordingly"
+    fi
 fi
 
 if test "$_os" = "AIX"; then