RFR: 8312121: Fix -Wconversion warnings in tribool.hpp [v2]

[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:

  Dean's suggestion.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14892/files
  - new: https://git.openjdk.org/jdk/pull/14892/files/73c2075a..c0e12b5d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14892&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14892&range=00-01

  Stats: 5 lines in 1 file changed: 0 ins; 3 del; 2 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