RFR: 8270179: Rename Amalloc_4 [v3]

[Coleen Phillimore]

> This renames Amalloc_4 to AmallocWords.  While I had to fix internal_malloc_4, which is a copy of Amalloc_4 (except with UseMallocOnly handling), I also made the change for
> JDK-8270217 Fix Arena::Amalloc to check for overflow better
> Tested with tier1 - all Oracle platforms and tier1-3 on linux-x64.

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

  Add more info why UseMallocOnly is useful.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4750/files
  - new: https://git.openjdk.java.net/jdk/pull/4750/files/dfd64c57..b49f5860

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4750&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4750&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4750.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4750/head:pull/4750

PR: https://git.openjdk.java.net/jdk/pull/4750