RFR: 8307316: Let JavaFX be built on unknown architectures

[John Neffenger]

Please review these changes to the Gradle build files and the dependency verification file. The initial version of this pull request extends the permitted build platforms for Linux to the Java architectures `arm`, `ppc64le`, and `s390x` and adds an entry to the dependency verification file for the `i386` architecture. The Debian names for these architectures are `armhf`, `i386`, `ppc64el`, and `s390x`.

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Commit messages:
 - Warn instead of failing on unknown architectures
 - Merge branch 'master' into allow-armhf-i386-ppc64el-s390x
 - Merge branch 'master' into allow-armhf-i386-ppc64el-s390x
 - Allow building on armhf, i386, ppc64el, and s390x

Changes: https://git.openjdk.org/jfx/pull/1124/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1124&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307316
  Stats: 9 lines in 3 files changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1124.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1124/head:pull/1124

PR: https://git.openjdk.org/jfx/pull/1124