RFR: 8247909: Improve PrimitiveConversions::cast using C++14 [v4]

[Kim Barrett]

> Please review this reimplementation of PrimitiveConversions::cast,
> using facilities from C++14.  In particular, conversions involving
> only integral values or integral and enum values are now constexpr.
> Also using <type_traits> rather than HotSpot work-alikes.
> 
> Had to update zForwardingEntry.hpp because of a class no longer being
> implicitly included.  Improved a friend declaration while in the
> vicinity.
> 
> Testing
> mach5 tier1

Kim Barrett 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 four additional commits since
the last revision:

 - Merge branch 'master' into update_primitive_conversions
 - fix implict dependency by test on integralConstant.hpp
 - fix comment
 - Reimpliment PC::cast, with some cases now constexpr.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/143/files
  - new: https://git.openjdk.java.net/jdk/pull/143/files/c55dfce8..174dbec3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=143&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=143&range=02-03

  Stats: 5387 lines in 118 files changed: 3393 ins; 1472 del; 522 mod
  Patch: https://git.openjdk.java.net/jdk/pull/143.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/143/head:pull/143

PR: https://git.openjdk.java.net/jdk/pull/143