RFR: 8377185: [iOS] Native code compiler warnings and error building libprism_es2 [v3]

[Jose Pereda]

> This PR fixes the errors and some warnings that are thrown when building prism_es2 for iOS using clang.

Jose Pereda has updated the pull request incrementally with one additional commit since the last revision:

  Unify defines in PrismES2Defs header

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Changes:
  - all: https://git.openjdk.org/jfx/pull/2064/files
  - new: https://git.openjdk.org/jfx/pull/2064/files/4c3dc446..a14d7938

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=2064&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=2064&range=01-02

  Stats: 20 lines in 3 files changed: 8 ins; 10 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/2064.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2064/head:pull/2064

PR: https://git.openjdk.org/jfx/pull/2064