RFR: 8234773: Fix ThreadsSMRSupport::_bootstrap_list [v2]

[Kim Barrett]

> Please review this change to ThreadsList and the singleton _bootstrap_list.
> ThreadsList is made noncopyable, with _bootstrap_list changed to be direct
> initialized to avoid referencing the copy constructor.  The ThreadsList
> constructor now uses a static array for the 0-entry case, so that static
> ctor/dtor of _bootstrap_list doesn't involve C-heap allocation.
> 
> Testing:
> mach5 tier1
> 
> Local (linux-x64) build with -fno-elide-constructors and ran hotspot:tier1.
> This has a failure unrelated to this change:
> compiler/intrinsics/klass/CastNullCheckDroppingsTest.java fails with
> #  Internal Error (../../src/hotspot/share/jfr/utilities/jfrVersionSystem.inline.hpp:98), pid=31086, tid=31713
> #  assert(node->_live) failed: invariant
> Filed new bug: https://bugs.openjdk.java.net/browse/JDK-8259036

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  Make ThreadsList constructor explicit.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1921/files
  - new: https://git.openjdk.java.net/jdk/pull/1921/files/d3240a18..1a6cbcb9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1921&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1921&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1921.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1921/head:pull/1921

PR: https://git.openjdk.java.net/jdk/pull/1921