openjdk: test build with llvm@17

[carlocab]

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Let's test whether this builds with llvm@17 to help track down the
build failure with Apple Clang 16.

[carlocab]

Seems to succeed: https://github.com/Homebrew/homebrew-core/actions/runs/10886892015/job/30208111641?pr=190817#step:3:38

CC @Bo98

[Bo98]

Current theory is an optimisation bug. Seems to not happen with slowdebug which I think uses -O0. Not sure which -O level triggers it.

[carlocab]

Ok, will add -Os to cflags and cxxflags next to see

[cho-m]

May be related root cause for OpenJDK 11 and 17, though for those a JVM crash happens during build. From local attempt for OpenJDK 17, need to go down to -O1 to avoid (though hard to test other LLVM since older OpenJDK uses a header that is not shipped in brew LLVM).

[Bo98]

Yeah seems to be -O2. Trying to pin it down further to a specific optimisation pass or what bit of code is failing but haven't gotten anywhere yet.

The default is -O3 for certain performance critical parts of the JVM so -O1 would be a big drop.

[Bo98]

With that said, if it's crashing in OpenJDK 17 it might be easier to debug properly there rather than it raising Java errors.