distrib/package-release.sh: Better change reports + arm64 launcher.

This patch improves the implementation of the --copy-prebuilts=<path>
option in package-release.sh. Most notably, a summary of all changes
since the last update is automatically generated with a command like:

  git log --oneline --no-merges <old-sha1>..<new-sha1>

For every relevant source directory. This makes it considerably
easier to see what changes between revisions of the prebuilt
binaries.

+ Copy the emulator64-arm64 binary (a QEMU launcher/wrapper really)
  when it is available.

Change-Id: I0e7fd3236ffa8016a9ea62c14e56c3fa68fdae74
1 file changed