RFR: 8326433: Make libjdwp and libjava closeDescriptors() as static function [v2]

[Jiangli Zhou]

> Please help review this trivial fix for resolving `ld: error: duplicate symbol: closeDescriptors` when static linking with both libjdwp and libjava, thanks.

Jiangli Zhou has updated the pull request incrementally with two additional commits since the last revision:

 - Address plummercj's comment and make forkedChildProcess static.
 - Revert src/java.base/unix/native/libjava/childproc.c and src/java.base/unix/native/libjava/childproc.h. Will handle those with JDK-8326714.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18013/files
  - new: https://git.openjdk.org/jdk/pull/18013/files/bb9e2791..3816d315

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18013&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18013&range=00-01

  Stats: 3 lines in 3 files changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18013.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18013/head:pull/18013

PR: https://git.openjdk.org/jdk/pull/18013