This is used to reduce the number of distributable prebuilt packages
(i.e. linux-x86_64 is not needed anymore).
Also fix build/tools/build-toolchain.sh to properly copy the GPL and LGPL
license files into the generated prebuilt packages.
Also add a .gitignore files to get less spew from 'git status'
Now you need to use the --prebuilt-path=<path> option to specify where to pick up
the prebuilt toolchain tarballs instead, for example:
build/tools/make-release.sh --prebuilt-path=/home/digit/android/ndk
Add also some other options to change the package prefix / release number / etc
