RFR: 8327460: Compile tests with the same visibility rules as product code [v2]

[Magnus Ihse Bursie]

> Currently, our symbol visibility handling for tests are sloppy; we only handle it properly on Windows. We need to bring it up to the same levels as product code. This is a prerequisite for [JDK-8327045](https://bugs.openjdk.org/browse/JDK-8327045), which in turn is a building block for Hermetic Java.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Update line number for dereference_null  in TestDwarf

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18135/files
  - new: https://git.openjdk.org/jdk/pull/18135/files/1dc79758..b1bf01ad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18135&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18135&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18135.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18135/head:pull/18135

PR: https://git.openjdk.org/jdk/pull/18135