RFR: 8343205: CompileBroker::possibly_add_compiler_threads excessively polls available memory

[Martin Doerr]

This PR adds a quick check + bail out in order to avoid excessive usage of slow checks. Especially, it avoids querying the available memory so often.

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Commit messages:
 - 8343205: CompileBroker::possibly_add_compiler_threads excessively polls available memory

Changes: https://git.openjdk.org/jdk/pull/21812/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21812&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343205
  Stats: 20 lines in 1 file changed: 14 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21812.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21812/head:pull/21812

PR: https://git.openjdk.org/jdk/pull/21812