[jdk17u] RFR: 8258465: Headless build fails due to missing X11 headers on linux

[Alexey Pavlyutkin]

I'd like to backport JDK-8258465 to jdk17u. The changes make configure to look up for X11 header that are REQUIRED even for HEADLESS builds.

The original patch applied cleanly

Tested with

-temporary rename your X11 include directory (usually /usr/include/X11)
-configure headless-only build with --enable-headless-only flag

EXPECTED result: configuration FAILS with

`configure: error: Could not find X11 libraries. You might be able to fix this by running 'sudo apt-get install libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev'.`

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Commit messages:
 - Backport 596b075591c4b2fe01bee7142f4d0a5f892647ed

Changes: https://git.openjdk.java.net/jdk17u/pull/215/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=215&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/jdk17u/pull/215.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/215/head:pull/215

PR: https://git.openjdk.java.net/jdk17u/pull/215