RFR: 8375311: Some builds are missing debug helpers

[Matthias Baesken]

[JDK-8318834](https://bugs.openjdk.org/browse/JDK-8318834) pointed out that on linux s390x, debug builds were missing debug helpers .
This happened because we enabled some time ago linktime gc (-Wl,--gc-sections in the linker flags, plus -ffunction-sections -fdata-sections in compile flags) for linux x390x by default.
But potentially ltgc or similar size-optimizing options could be enabled on other platforms too, and not only debug builds could lose the debug helpers (however in non-debug builds they might be not that important).

On Windows we already export the debug helper symbols, so it might be good to do this on other platforms, especially Linux, too.

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Commit messages:
 - JDK-8375311

Changes: https://git.openjdk.org/jdk/pull/29232/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29232&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375311
  Stats: 6 lines in 1 file changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/29232.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29232/head:pull/29232

PR: https://git.openjdk.org/jdk/pull/29232