RFR: 8253779: Amalloc may be wasting space by overaligning [v4]

[Coleen Phillimore]

> Thanks to @kimbarrett for noticing this. The alignment was changed to 64 bits for 32 bit platforms, but overalign for 64 bits platforms.  I changed this to BytesPerLong to cover both, since the long case is why it was changed on 32 bits in the first place in JDK-4526490.
> I also removed Amalloc_D since I don't know what D stands for and it's the same as Amalloc_4.  That's not a great name either. I'm open to suggestions!
> Tested with tier1-3.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Fix ARENA_ALIGN macro

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4732/files
  - new: https://git.openjdk.java.net/jdk/pull/4732/files/220c3cb8..7ebc7421

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4732&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4732&range=02-03

  Stats: 6 lines in 1 file changed: 1 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4732.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4732/head:pull/4732

PR: https://git.openjdk.java.net/jdk/pull/4732