[ARM] fixup path to NDK dir.
[ARM] fixup path to NDK dir.

AOSP moved the location of NDKs to prebuilts.

(on older branches, such as JB, may also need to download
android-ndk-r8, since it is not in-tree.)

paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank,paul99/clank