RFR: 8257758: Allow building of JavaFX native libs for Apple Silicon [v2]

[Johan Vos]

> Fix for JDK-8257758
> 
> In case the -PtargetArch=arm64 option is supplied to the gradle build, the
> native components that are part of the JavaFX build will target this platform.

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

  process reviewer comments

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/363/files
  - new: https://git.openjdk.java.net/jfx/pull/363/files/1e695699..36becd31

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=363&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=363&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/363.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/363/head:pull/363

PR: https://git.openjdk.java.net/jfx/pull/363