RFR: 8283298: Make CodeCacheSegmentSize a product flag

[Jie Fu]

Hi all,

As discussed in https://github.com/openjdk/jdk/pull/7830, this patch makes `CodeCacheSegmentSize` a product flag.
It also fixes two bugs when testing the release VM with CodeEntryAlignment={512, 1024}.
Please review it.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8283298: Make CodeCacheSegmentSize a product flag

Changes: https://git.openjdk.java.net/jdk/pull/7851/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7851&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283298
  Stats: 10 lines in 4 files changed: 4 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7851.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7851/head:pull/7851

PR: https://git.openjdk.java.net/jdk/pull/7851