[jdk8u] RFR: 8304143: Exclude duplicated class on linux, aix, and macos

[Adam Farley]

This change excludes the duplicated class SystemMetrics, and ensures we use the platform-specific version of the SystemMetrics class instead.

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Commit messages:
 - 8304143 - Exclude duplicated class on linux, aix, and macos

Changes: https://git.openjdk.org/jdk8u/pull/40/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u&pr=40&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304143
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk8u/pull/40.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u pull/40/head:pull/40

PR: https://git.openjdk.org/jdk8u/pull/40