RFR: New test for direct byte buffers

[Andrew Dinn]

As requested, I have created some new tests for direct byte buffers
which are submitted via the following PR:

  https://github.com/graalvm/graal/pull/229

This passes unit test on x86 and AArch64.

Also, I reverted the tweak to the AArch64 address lowering patch and
found that it failed on AArch64 as expected i.e. it would have caught
the original error (yeah, I also eyeballed the generated code and it did
indeed fail for the expected reason).

regards,


Andrew Dinn
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