Set up CMake build for extension/evalue_util

[swolchok]

It didn't have one. Now it does.

[swolchok]

arm-cortex-m-size-test appears to have failed more than once now with

In file included from /pytorch/executorch/extension/data_loader/mmap_data_loader.cpp:19:
/pytorch/executorch/extension/data_loader/../../../executorch/extension/data_loader/mman.h:18:10: fatal error: sys/mman.h: No such file or directory
18 | #include <sys/mman.h>

puzzling, will have to investigate. other tests are looking pretty good; test-llama-runner-mac (fp32, coreml) looks like it's probably either a flake or a different PR because it's an output change, which this PR really should not cause.

[swolchok]

will have to investigate.

repros on previous PR #12678

does not repro on #12667.

Moving investigation to #12678

[swolchok]

test-llama-runner-mac (fp32, coreml) is still failing! very strange

[swolchok]

test-models-linux-basic mv3 failure https://github.com/pytorch/executorch/actions/runs/16456606096/job/46515099970?pr=12691 failure looks like an infra flake

test-llama-runner-mac (fp32, coreml) is still failing! very strange

failure does not repro locally

[swolchok]

test-llama-runner-mac (fp32, coreml) is still failing! very strange

failure does not repro locally

passing now, must've been some weird transient issue

[swolchok]

merging based on previous good CI run