RFR: JDK-8267916: Make as_CompilerThread consistent with other as_*_thread methods [v2]

[Albert Mingkun Yang]

> Simple refactoring around `as_CompilerThread`. A new file, `compilerThread.inline.hpp`, is created to get around the circular dependency.

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  cast

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4240/files
  - new: https://git.openjdk.java.net/jdk/pull/4240/files/cc3141b2..c919ae36

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4240&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4240&range=00-01

  Stats: 66 lines in 14 files changed: 9 ins; 52 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4240.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4240/head:pull/4240

PR: https://git.openjdk.java.net/jdk/pull/4240