determine fht_avx.c/fht_neon.c based on CMake target processor

[swolchok]

Might fix#6691.

[swolchok]

Stack from ghstack (oldest at bottom):

• build_variables.bzl: split PLATFORM_SRCS from EXECUTORCH_CORE_SRCS #8398
• build_variables.bzl: split PROGRAM_NO_PRIM_OPS_SRCS from EXECUTORCH_CORE_SRCS #8397
• create and validate build_variables.bzl #8326
• ->determine fht_avx.c/fht_neon.c based on CMake target processor #8346
• Add extension/llm/custom_ops/spinquant/test to CMake #8345
• Bypass find_package(torch) for find_package_torch_headers to help out cross compilation #8629

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/8346

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

✅ You can merge normally! (1 Unrelated Failure)

As of commit 8df2f1d with merge base f3fc096 ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-llava-runner-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[jackzhxng]

My comment is irrelevant since you are removing it, but this second regex seemed wrong?

[swolchok]

Looks right to me. Dot is a regex metacharacter so we need to escape it with a backslash. Backslash is a string metacharacter so we need to escape it with a second backslash. Or is there a different problem I missed entirely?