i#1966 ARM/AArch64 testing: Add cross-compiling builds.
i#1966 ARM/AArch64 testing: Add cross-compiling builds.

We install the two cross-compiler packages on Linux.

Review-URL: https://codereview.appspot.com/306130043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio