RFR: JDK-8300069: Left shift of negative value in share/adlc/dict2.cpp

[Justin King]

Refactor `hashstr` to use unsigned integrals to avoid undefined behavior.

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Commit messages:
 - Left shift of negative value in share/adlc/dict2.cpp

Changes: https://git.openjdk.org/jdk/pull/11977/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11977&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300069
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/11977.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11977/head:pull/11977

PR: https://git.openjdk.org/jdk/pull/11977