RFR: Add flag to prevent multiple deopts on the same nmethod. [v3]

[Coleen Phillimore]

> I added a flag to prevent the same nmethod from being optimized multiple times.  It might be better to have a new MarkForDeoptimizationStatus enum but wasn't sure how that would interact with the deoptimize_update state.  Advice welcome.
> I also don't know why the sweeper is so slow to get rid of these entries.
> This makes ctw_2 test run in an hour on my machine, just like mainline jdk/jdk (machine is slow!) in fastdebug.

Coleen Phillimore 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 three additional commits since the last revision:

 - Merge branch 'fibers' into ctw
 - This is better imo.
 - Add flag to prevent multiple deopts on the same nmethod.

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/81/files
  - new: https://git.openjdk.java.net/loom/pull/81/files/cb8b8925..0d998c61

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=81&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=81&range=01-02

  Stats: 21948 lines in 709 files changed: 16317 ins; 2922 del; 2709 mod
  Patch: https://git.openjdk.java.net/loom/pull/81.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/81/head:pull/81

PR: https://git.openjdk.java.net/loom/pull/81