[master] RFR: Fix arrays-equals intrinsic on AArch64

[Roman Kennke]

The arrays-equals intrinsic on AArch64 assumes that array elements start at 8-byte-aligned boundary. There are several problems with that:
- Doing unaligned loads is likely rather slow.
- I believe it may give wrong results when comparing some junk after the end of the array.
- We may crash when loading beyond the heap boundary.

The proposed fix is to start the comparison at the array-length field. When the array base is unaligned (that is really 4-byte-aligned), then the array-length is at 8-byte-aligned location. And since we want to compare the lengths anyway, we can just as well use word-sized loads to compare the length and first elements in a single step, and elide the separate cmp+branch for the length.

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Commit messages:
 - Fix arrays-equals intrinsic on AArch64

Changes: https://git.openjdk.org/lilliput/pull/170/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=170&range=00
  Stats: 42 lines in 1 file changed: 33 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/lilliput/pull/170.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/170/head:pull/170

PR: https://git.openjdk.org/lilliput/pull/170