RFR: 8193559: ugly DO_JAVA_THREADS macro should be replaced

[Daniel D.Daugherty]

This is a simple rewrite of what is "Possibly the ugliest for loop the world has seen."
Thanks to @stefank for the draft proposed fix. Thanks to @fisk for providing this
piece of history that I'm finally getting around to cleaning up. While this macro has
been with us for a long time, its time has passed...

Tested with Mach5 Tier[1-3].

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Commit messages:
 - 8193559.cr0

Changes: https://git.openjdk.java.net/jdk/pull/4671/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4671&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8193559
  Stats: 22 lines in 1 file changed: 8 ins; 0 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4671.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4671/head:pull/4671

PR: https://git.openjdk.java.net/jdk/pull/4671