RFR: 8255723: Gtk glass backend should run with Gtk+ 3.8 (minimum)

[Thiago Milczarek Sayao]

Simple fix to not build with GTK+ greater than 3.8 symbols.

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Commit messages:
 - Fix minimum GTK version (glass DND)
 - Merge pull request #13 from openjdk/master
 - Merge pull request #12 from openjdk/master
 - Merge pull request #11 from openjdk/master
 - Merge pull request #10 from openjdk/master
 - Merge pull request #9 from openjdk/master
 - Merge pull request #8 from openjdk/master
 - Merge pull request #7 from openjdk/master
 - Merge pull request #6 from openjdk/master
 - Merge pull request #5 from openjdk/master
 - ... and 1 more: https://git.openjdk.java.net/jfx/compare/cb545cc6...4f589df9

Changes: https://git.openjdk.java.net/jfx/pull/346/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=346&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255723
  Stats: 4 lines in 1 file changed: 0 ins; 4 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/346.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/346/head:pull/346

PR: https://git.openjdk.java.net/jfx/pull/346