RFR: 8323242: Remove vestigial DONT_USE_REGISTER_DEFINES

[Guoxiong Li]

On Tue, 5 Mar 2024 08:07:19 GMT, Koichi Sakata <ksakata at openjdk.org> wrote:

> This pull request removes an unnecessary directive.
> 
> There is no definition of DONT_USE_REGISTER_DEFINES in HotSpot or the build system, so this `#ifndef`conditional directive is always true. We can remove it. 
> 
> I built OpenJDK with Zero VM as a test. It was successful.
> 
> 
> $ ./configure --with-jvm-variants=zero --enable-debug
> $ make images 
> $ ./build/macosx-aarch64-zero-fastdebug/jdk/bin/java -version                                                                                                                                         
> openjdk version "23-internal" 2024-09-17                                                                                                                                                                                                                                                 
> OpenJDK Runtime Environment (fastdebug build 23-internal-adhoc.jyukutyo.jyukutyo-jdk)                                                                                                                                                                                                    
> OpenJDK 64-Bit Zero VM (fastdebug build 23-internal-adhoc.jyukutyo.jyukutyo-jdk, interpreted mode)
> 
> 
> It may be possible to remove the `#define noreg` as well because the CONSTANT_REGISTER_DECLARATION macro creates a variable named noreg, but I can't be sure. When I tried removing the noreg definition and building the OpenJDK, the build was successful.

Looks good.

Some related issues:
[JDK-8269122](https://bugs.openjdk.org/browse/JDK-8269122)
[JDK-8282085](https://bugs.openjdk.org/browse/JDK-8282085)
[JDK-8200168](https://bugs.openjdk.org/browse/JDK-8200168)
[JDK-8297445](https://bugs.openjdk.org/browse/JDK-8297445)

Please fix the title of the issue or this PR.

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

Marked as reviewed by gli (Committer).

PR Review: https://git.openjdk.org/jdk/pull/18115#pullrequestreview-1917283298
PR Comment: https://git.openjdk.org/jdk/pull/18115#issuecomment-1978967341