Download the NDK only the first time

builds/android/ci_build.sh

@@ -14,12 +14,14 @@ else
     exit 1
 fi
 
-export FILENAME=$NDK_VERSION-$HOST_PLATFORM.zip
+if [ ! -d "/tmp/${NDK_VERSION}" ] ; then
+    export FILENAME=$NDK_VERSION-$HOST_PLATFORM.zip
 
-(cd '/tmp' \
-    && wget http://dl.google.com/android/repository/$FILENAME -O $FILENAME \
-    && unzip -q $FILENAME) || exit 1
-unset FILENAME
+    (cd '/tmp' \
+        && wget http://dl.google.com/android/repository/$FILENAME -O $FILENAME \
+        && unzip -q $FILENAME) || exit 1
+    unset FILENAME
+fi
 
 function _build_arch {
     export ANDROID_NDK_ROOT="/tmp/${NDK_VERSION}"