Fix GraalVM flag selection when USE_MEOWICE_FLAGS is not set

[OowhitecatoO]

Fixes #3881.

Setting USE_MEOWICE_GRAALVM_FLAGS=true without also setting USE_MEOWICE_FLAGS makes the JVM exit at startup on any GraalVM 25 image: Error parsing Graal options: Could not find option OptWriteMotion. This reproduces on the currently published java25-graalvm tag, so it is not tied to the variants being rebuilt.

java_major_version is assigned at start-finalExec:217, inside the USE_MEOWICE_FLAGS guard, but it is read at :350 inside the USE_MEOWICE_GRAALVM_FLAGS block. With only the latter set the variable is never assigned, and since an unset value compares as 0, [[ $java_major_version -gt 23 ]] is false and the pre-Java-24 flag set is emitted — including -Dgraal.OptWriteMotion=true, which GraalVM removed in 25 and whose parser treats an unknown option as fatal.

This assigns the version when either flag is set. The other three combinations emit exactly the same command line as before.

Details, if useful

-Dgraal.OptWriteMotion=true passed to java -version directly:

image	result
Oracle GraalVM 21.0.12	starts, exit 0
Oracle GraalVM 25.0.4	Could not find option OptWriteMotion, A fatal exception has occurred, exit 1
itzg/minecraft-server:java25-graalvm as published (25.0.1)	same, exit 1

Which branch each combination takes, checked with SETUP_ONLY=true on a GraalVM 25 image and reading the printed SETUP_ONLY: java ... line:

USE_MEOWICE_FLAGS	USE_MEOWICE_GRAALVM_FLAGS	branch	OptWriteMotion emitted
unset	unset	block skipped	no
set	unset	block skipped	no
unset	set	Using MeowIce's flags for Graalvm	yes — the failure
set	set	Java 24 or higher detected	no

With this change the third row becomes Java 24 or higher detected and stops emitting the option; the other three rows are unchanged, which I checked by diffing the printed command lines. The modern flag set on its own was also run against GraalVM 25.0.4 to confirm it starts cleanly.

Verification used the script mount from the development docs — -v .../start-finalExec:/image/scripts/start-finalExec:ro — rather than rebuilding, and bash -n passes on the modified script.

Choosing USE_MEOWICE_FLAGS || USE_MEOWICE_GRAALVM_FLAGS rather than hoisting the assignment unconditionally keeps mc-image-helper java-release from running on every start for the majority of users who set neither.

[itzg]

Thanks! I was hopeful it was a simple thing like that.