RFR: 8312121: Fix -Wconversion warnings in tribool.hpp [v5]

[Coleen Phillimore]

> Assigning _value first, and then doing _value | 2 doesn't get -Wconversion warnings.  Also, reduced include file inclusion a little.
> Tested with tier1 on linux-x64-debug, windows-x64-debug, macos-aarch64-debug

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Back to V1.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14892/files
  - new: https://git.openjdk.org/jdk/pull/14892/files/f135916d..d380e8ef

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14892&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14892&range=03-04

  Stats: 7 lines in 1 file changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/14892.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14892/head:pull/14892

PR: https://git.openjdk.org/jdk/pull/14892