RFR: 8295811: serviceability/sa/TestObjectAlignment.java fails on x86_32

[Jie Fu]

It fails on x86_32 due to `Unrecognized VM option ObjectAlignmentInBytes=8`.
So let's only run the test on 64-bit platforms.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8295811: serviceability/sa/TestObjectAlignment.java fails on x86_32

Changes: https://git.openjdk.org/jdk/pull/10829/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10829&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295811
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10829.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10829/head:pull/10829

PR: https://git.openjdk.org/jdk/pull/10829