RFR: 8275265: java/nio/channels tests needing large heap sizes fail on x86_32

[Jie Fu]

Hi all,

java/nio/channels/FileChannel/LargeGatheringWrite.java and java/nio/channels/Channels/ReadXBytes.java fail on x86_32.

This is because they require `-Xmx4G` and `-Xmx8G`, which are invalid on 32-bit platforms.
So let's exclude them on 32-bit platforms.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8275265: Two java/nio/channels tests fails on x86_32

Changes: https://git.openjdk.java.net/jdk/pull/5942/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5942&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275265
  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5942.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5942/head:pull/5942

PR: https://git.openjdk.java.net/jdk/pull/5942