JEP draft: Deprecate the Windows x86-32 Port

Summary

Deprecate the Windows x86-32 port, with the intent to remove it in a future release.

Motivation

Dropping support for this port will enable contributors in the OpenJDK Community to accelerate the development of new features that will move the platform forward. There is currently no implementation of JEP 436 (Virtual Threads) for 32-bit platforms and without a vendor stepping forward to implement this it's unlikely that OpenJDK will be able to continue supporting 32-bit architectures. Another motivation is that Windows 10 (the last Windows operating system to support a 32-bit installation) will reach EOL on October 14, 2025. The main focus of this JEP is to deprecate the Windows x86 port.

Goals

The proposal has the following goals:

1. Enhance the build system to issue an error message when an attempt is made to configure a build for the deprecated port. The error message will be suppressible via a new configuration option.
2. Mark the port, and related port-specific features, as deprecated for removal in the relevant JDK documentation.

Non-Goals

1. It is not a goal of this JEP to change the status of the affected port in any prior release. The earliest release to which this JEP could be targeted is JDK 21.

Description

Build-configuration changes

An attempt to configure a Windows x86-32 build will produce the following output:

$ bash ./configure
...
checking compilation type... native
configure: error: The Windows x86-32 port is deprecated and may be removed in a future release. \
Use --enable-deprecated-ports=yes to suppress this error.
configure exiting with result code 1
$

The new build-configuration option --enable-deprecated-ports=yes will suppress the error and continue:

$ bash ./configure --enable-deprecated-ports=yes
...
checking compilation type... native
configure: WARNING: The Windows x86-32 port is deprecated and may be removed in a future release.
...
Build performance summary:
* Cores to use:   32
* Memory limit:   96601 MB

The following warnings were produced. Repeated here for convenience:
WARNING: The Windows x86-32 port is deprecated and may be removed in a future release.
$

The error/warning will be issued when configuring a build for Windows x86-32.

A proposed webrev is available showing the 3 changes (total 22 lines) to the following files:

• doc/building.html
• doc/building.md
• make/autoconf/platform.m4

Alternatives

Just as with JEP 362 (Deprecate the Solaris and SPARC Ports), an alternative is for a set of credible developers to express a clear desire to maintain this port going forward including but not limited to creating an implementation of Virtual Threads for x86-32. If that happens before this JEP is integrated then this JEP can be withdrawn. If that happens after this JEP is integrated, but before the ports are removed, then a follow-on JEP can revert the deprecation.