Image test failure on linux/darwin amd64 with -o:speed on LLVM 17 & 18

[laytan]

Context

While trying to verify #3308 by running all tests with optimisations turned on, I found this test failure that has been there for a while already. I couldn't figure it out in reasonable time there, so I am making this issue.

Reproduced on Linux and Darwin amd64, with -o:speed on LLVM 17 and 18.

There is even a comment by @Kelimion in the test file mentioning failure

Odin/tests/core/image/test_core_image.odin

Line 1494 in c72a269

// This struct compare fails at -opt:2 if PNG_Dims is not #packed.

Steps to Reproduce

odin run tests/core/image -o:speed