RFR: 8255216: ciEnv::_break_at_compile isn't in use [v5]

[Dan]

> _break_at_compile is no longer in use and can be safely removed.
> No new code, and Tier1 tests succeed after code is removed.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8255216

Dan has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains two new commits since the last revision:

 - Revert "8255216: ciEnv::_break_at_compile isn't in use"
   
   This reverts commit 4b783cca567ed2bb11e362144fa67bfd9d9cd043.
 - Address PR feedback + comments
   
   Move to env()->break_at_compile() in compile.cpp

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1806/files
  - new: https://git.openjdk.java.net/jdk/pull/1806/files/990634b9..41d01c05

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1806&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1806&range=03-04

  Stats: 11 lines in 3 files changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1806.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1806/head:pull/1806

PR: https://git.openjdk.java.net/jdk/pull/1806