RFR: 8274322: Problems with oopDesc construction

[Kim Barrett]

Please review this change to the default constructor for markWord and
associated "change" to construction of oopDesc.

The current code never invokes the constructor for oopDesc or any of its
derived classes.  For that to be permissible according to the Standard,
those classes must be trivially default constructible.  And for that to be
the case, the markWord default constructor must be trivial.

This change consists of three parts.

(1) The markWord default constructor is changed to be trivial, so the
default constructors for oopDesc and classes derived from it will also be
trivial. It wasn't previously trivial because the mechanism for making it so
(a default definition) is a C++11 feature that wasn't yet supported when the
previous constructor was defined.

(2) This change also adds static asserts to verify the relevant classes have
trivial default constructors, to prevent later changes from unintentionally
breaking this.

(3) This change also makes oopDesc noncopyable, to prevent inadvertent usage
of these operations that don't make any sense.

A different approach would be to always use placement new with an
appropriate constructor to perform the initialization, perhaps encapsulated
in factory functions.  I did some exploration in that direction. It's a much
larger and more complex change, though the final behavior (use constructors
for initialization) is simpler.

Testing:
tier1

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

Commit messages:
 - improve oopDesc and markWord construction

Changes: https://git.openjdk.java.net/jdk/pull/5729/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5729&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274322
  Stats: 32 lines in 5 files changed: 28 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5729.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5729/head:pull/5729

PR: https://git.openjdk.java.net/jdk/pull/5729