RFR: 8374521: Support fine-grained native debug levels

[Aleksey Shipilev]

[JDK-8374507](https://bugs.openjdk.org/browse/JDK-8374507) forced me to look into debug info sizes again. And I remembered that GCC actually have debug-level support, which can select what kind of diagnostic data is in the debug info. See: https://gcc.gnu.org/onlinedocs/gcc-4.5.0/gcc/Debugging-Options.html

Allowing users to configure the debug level allows two major deviations from the default level (2):
 level=1: significantly reduce the debug info size, but still allow backtrace reconstruction
 level=3: add even more debugging info, like macro expansion, into the debug data

This RFE upstreams the variant the patch that I have been using in builds.shipilev.net binaries: the fastdebug variants there are done with GCC level=1, greatly optimizing the debug binary sizes, while still maintaining the major benefit of debug binaries -- rich crash diagnostics.

I threw in this option into current GHA builds to conserve more disk space on runners and/or transfers. 

I am open for bikeshedding on the option name :)

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Commit messages:
 - Fallback when compiler does not support the value
 - Also enable in GHA
 - Debug levels

Changes: https://git.openjdk.org/jdk/pull/29056/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29056&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374521
  Stats: 25 lines in 5 files changed: 21 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29056.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29056/head:pull/29056

PR: https://git.openjdk.org/jdk/pull/29056