Add the Linaro GNU 4.9 Binary Toolchain

Add the Linaro GNU Binary Toolchain as a third party prebuilt.
This is needed for the aarch64 cross compiler (gcc), to
facilitate CI testing.

Signed-off-by: Fuad Tabba <tabba@google.com>
Change-Id: I75c3903155543d6bbc06d273f6db803cb0a465bd