RFR: 8352044: Add --with-import-jvms to configure

[Magnus Ihse Bursie]

On Fri, 14 Mar 2025 15:49:44 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> We should allow pre-built JVMs to be included in a build, so they are just copied into place, and the jvm.cfg file properly updated.

And to be absolutely clear: this PR is just about adding new functionality that was not present before.

A follow-up PR for JDK-8352045 will actually remove functionality from the build system. But, and once again, let me be absolutely clear, the intention is that even after that PR, any distributor who wants to build an image with multiple JVMs will still be able to do so. The generated bits will be identical before and after JDK-8352045; the only difference is that you are going to need a "pre-build" step for each additional JVM you want to add, where the pre-build step basically consists of calling `bash configure --with-jvm-variant=<my variant> && make hotspot`. If you add this simple step, you are going to get the exact same bits in the image.

In theory, I could even program a make target to call `configure --with-jvm-variant=<my variant> --with-conf-name=support-for-<my variant> && make hotspot CONF=support-for-<my variant>` but that's kind of silly, and looks like babysitting and insulting the intelligence of distributors...

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PR Comment: https://git.openjdk.org/jdk/pull/24063#issuecomment-2733054041
PR Comment: https://git.openjdk.org/jdk/pull/24063#issuecomment-2733057930