Preventing future MSVC 2012 surprises with SimpleArray by giving it an explicit move assignment operator.
[ARM64] Default to the 'generic' CPU, unless -arch is present for backwards compatibility.
[ARM64] Plumb in big-endian - add arm64_be to the many switches where it was missing.
[ARM64] Teach Targets.cpp about Cortex-A53 and Cortex-A57, and enable more tests.
[ARM64] Add ARM64 RUN lines to a bunch of tests that had AARCH64 RUN lines.

This covers all tests in tests/Driver and tests/Preprocessor, but there are some
failing tests in test/Sema that need looking into.
[ARM64] Fix __clear_cache - ensure it is predefined.