RFR: 8373388: Reenable LTO for libsplashscreen

[Matthias Baesken]

[JDK-8372554](https://bugs.openjdk.org/browse/JDK-8372554) disabled LTO for libsplashscreen to fix an issue with the comparison build. It turns out the failure was caused by extra files that LTO produced and which were included in the image. Now that [JDK-8373255](https://bugs.openjdk.org/browse/JDK-8373255) has fixed that we should be able to reenable LTO again.

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Commit messages:
 - JDK-8373388

Changes: https://git.openjdk.org/jdk/pull/28746/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28746&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373388
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28746.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28746/head:pull/28746

PR: https://git.openjdk.org/jdk/pull/28746