[jfx11u] RFR: 8280840: Update libFFI to 3.4.2

[Kevin Rushforth]

Clean backport to `jfx11u`. Tested in connection with gstreamer / glib update in the `test-kcr-11.0.16` branch.

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Commit messages:
 - 8280840: Update libFFI to 3.4.2

Changes: https://git.openjdk.java.net/jfx11u/pull/93/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=93&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280840
  Stats: 3475 lines in 34 files changed: 927 ins; 38 del; 2510 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/93.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/93/head:pull/93

PR: https://git.openjdk.java.net/jfx11u/pull/93