RFR: 8295847: slow debug build error after JDK-8294466

[Magnus Ihse Bursie]

[JDK-8294466](https://bugs.openjdk.org/browse/JDK-8294466) trimmed down the set of disabled warnings. Unfortunately it turned out that running slowdebug on linux on Oracle's CI triggered yet another warning in libsplashscreen.

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Commit messages:
 - 8295847: slow debug build error after JDK-8294466

Changes: https://git.openjdk.org/jdk/pull/10840/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295847
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10840.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10840/head:pull/10840

PR: https://git.openjdk.org/jdk/pull/10840