RFR: 8310920: Fix -Wconversion warnings in command line flags [v2]

[Coleen Phillimore]

> This is broken out from but tested with the PR from https://github.com/openjdk/jdk/pull/14659

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

  Make phase parameter JVMFlagConstraintPhase and fix another double/float conversion.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14665/files
  - new: https://git.openjdk.org/jdk/pull/14665/files/19baa252..95ee731c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14665&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14665&range=00-01

  Stats: 17 lines in 4 files changed: 0 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/14665.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14665/head:pull/14665

PR: https://git.openjdk.org/jdk/pull/14665