RFR: 8258465: Headless build fails due to missing X11 headers on linux

[Magnus Ihse Bursie]

It turned out that JDK-8255785 was incorrectly verified, and headless do indeed need X headers. This fix is a revert (anti-delta) of JDK-8255785.

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Commit messages:
 - 8258465: Headless build fails due to missing X11 headers on linux

Changes: https://git.openjdk.java.net/jdk/pull/5278/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5278&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258465
  Stats: 5 lines in 1 file changed: 1 ins; 3 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5278.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5278/head:pull/5278

PR: https://git.openjdk.java.net/jdk/pull/5278