RFR: 8292458: Atomic operations on scoped enums don't build with clang

[Kim Barrett]

Please review this change to allow the Atomic class to support scoped enum
values on all platforms.  We do this by adding PrimitiveConversions::Translate
support for enums (converting to/from the underlying type), and changing
relevant Atomic operations to use that translation instead of trying to handle
enums on the integer code path.

Testing:
mach5 tier1-3, including gtests added by this change

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Commit messages:
 - atomic ops use new enum translator
 - test atomics on enums

Changes: https://git.openjdk.org/jdk/pull/9895/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9895&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292458
  Stats: 128 lines in 4 files changed: 115 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/9895.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9895/head:pull/9895

PR: https://git.openjdk.org/jdk/pull/9895