RFR: 8322758: Eliminate -Wparentheses warnings in C2 code

[Kim Barrett]

Please review this change to eliminate some -Wparentheses warnings.  In most
cases, this involved simply adding a few parentheses to make some implicit
operator precedence explicit.

In PhaseIdealLoop::rc_predicate, I also added a comment describing the test
being performed, since it didn't seem obvious even with the additional
parentheses.

Testing: mach5 tier1

Also ran mach5 tier1 with these changes in conjunction enabling -Wparentheses
and other changes needed to make that work.

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

Commit messages:
 - fix -Wparentheses warnings in C2 code

Changes: https://git.openjdk.org/jdk/pull/17199/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17199&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322758
  Stats: 18 lines in 9 files changed: 2 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/17199.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17199/head:pull/17199

PR: https://git.openjdk.org/jdk/pull/17199