[lworld] RFR: 8281618: Add asmtools sources as a test library [v2]

[Dan Smith]

> This is mostly a direct copy of the asmtools repo. The one interesting file is JtregDriver, which avoids various complications involved in directly invoking the asmtools 'Main' entry point.

Dan Smith has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge branch 'lworld' into asmtools
 - Fix trailing whitespace
 - Added usage comment
 - Generalize JtregDriver for all asmtools commands
 - Add JtregDriver to provide an entry point that doesn't call System.exit
 - Add asmtools source to test/lib

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

Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/646/files
  - new: https://git.openjdk.java.net/valhalla/pull/646/files/ccbec02f..ed43e819

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=646&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=646&range=00-01

  Stats: 106967 lines in 2913 files changed: 70406 ins; 20833 del; 15728 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/646.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/646/head:pull/646

PR: https://git.openjdk.java.net/valhalla/pull/646