RFR: 8247909: Improve PrimitiveConversions::cast using C++14 [v3]

[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 incrementally with one additional commit since the last revision:

  fix implict dependency by test on integralConstant.hpp

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/143/files
  - new: https://git.openjdk.java.net/jdk/pull/143/files/f451696d..c55dfce8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=143&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=143&range=01-02

  Stats: 4 lines in 1 file changed: 2 ins; 1 del; 1 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