RFR: Add flag to prevent multiple deopts on the same nmethod. [v2]

[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 incrementally with one additional commit since the last revision:

  This is better imo.

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Changes:
  - all: https://git.openjdk.java.net/loom/pull/81/files
  - new: https://git.openjdk.java.net/loom/pull/81/files/5dfd79e1..cb8b8925

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=81&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=81&range=00-01

  Stats: 9 lines in 2 files changed: 3 ins; 2 del; 4 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