RFR: 8326509: Clean up JNIEXPORT in Hotspot after JDK-8017234 [v5]

[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 incrementally with three additional commits since the last revision:

 - Why did these creep back in? Merge error?
 - Remove #undef JNIEXPORT
 - Remove das1()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17967/files
  - new: https://git.openjdk.org/jdk/pull/17967/files/43c3513b..387d243b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17967&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17967&range=03-04

  Stats: 24 lines in 4 files changed: 0 ins; 24 del; 0 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