This is a breakout from [JDK-8293114](https://bugs.openjdk.org/browse/JDK-8293114), which is starved for reviews. So I attempt to break up that fix into smaller units which are hopefully easier to review separately.
We can trim the C-heap manually using jcmd since [JDK-8268893](https://bugs.openjdk.org/browse/JDK-8268893). This patch reshapes this code, cleaning it up in an OS-agnostic way. That will allow us to add implementions for other platforms (I have this on my list for AIX at least) and make review of 8293114 easier. ------------- Commit messages: - JDK-8296796-factor-out-os-trim-native-heap Changes: https://git.openjdk.org/jdk/pull/11089/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11089&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8296796 Stats: 141 lines in 10 files changed: 89 ins; 34 del; 18 mod Patch: https://git.openjdk.org/jdk/pull/11089.diff Fetch: git fetch https://git.openjdk.org/jdk pull/11089/head:pull/11089 PR: https://git.openjdk.org/jdk/pull/11089
