[jfx21u] RFR: 8278021: Fix warnings in macOS glass native code and treat warnings as errors [v2]

[Johan Vos]

> Hi all,
> 
> This pull request contains a backport of commit [e0b88bc7](https://github.com/openjdk/jfx/commit/e0b88bc7cfede46afe28cbb4a2e333df933b5100) from the [openjdk/jfx](https://git.openjdk.org/jfx) repository.
> 
> The commit being backported was authored by Martin Fox on 22 Feb 2024 and was reviewed by Kevin Rushforth and Ajit Ghaisas.
> 
> Thanks!

Johan Vos has updated the pull request incrementally with one additional commit since the last revision:

  Do not use -Werror on jfx21u

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

Changes:
  - all: https://git.openjdk.org/jfx21u/pull/114/files
  - new: https://git.openjdk.org/jfx21u/pull/114/files/057b6641..52bbe438

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx21u&pr=114&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx21u&pr=114&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jfx21u/pull/114.diff
  Fetch: git fetch https://git.openjdk.org/jfx21u.git pull/114/head:pull/114

PR: https://git.openjdk.org/jfx21u/pull/114