RFR: 8326509: Clean up JNIEXPORT in Hotspot after JDK-8017234 [v3]

[Magnus Ihse Bursie]

> Once [JDK-8017234](https://bugs.openjdk.org/browse/JDK-8017234) has been integrated, it is possible to do some cleanup. The goal of [JDK-8017234](https://bugs.openjdk.org/browse/JDK-8017234) was to not change any behavior, even if that behavior seemed odd.
> 
> Now let's try to fix that. We can:
> 
> a) remove JNIEXPORT from c2v functions.
> b) make debug.cpp functions exported similarly on all platforms.
> c) remove JNIEXPORT from aarch64 asm debug function.
> 
> Note that this PR is [dependent on](https://mail.openjdk.org/pipermail/jdk-dev/2021-March/005232.html) https://github.com/openjdk/jdk/pull/17955.

Magnus Ihse Bursie has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Remove jvmci globals
 - 8326509: Clean up JNIEXPORT in Hotspot after JDK-8017234

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/17967/files
  - new: https://git.openjdk.org/jdk/pull/17967/files/216d0db5..b6bd5f22

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17967&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17967&range=01-02

  Stats: 31 lines in 1 file changed: 4 ins; 7 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/17967.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17967/head:pull/17967

PR: https://git.openjdk.org/jdk/pull/17967