Don't build MmapDataLoader if sys/mman.h isn't available and we're not on Windows

[swolchok]

It won't work in this case.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12743

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❌ 7 New Failures, 3 Unrelated Failures

As of commit e0183db with merge base cfefd2c ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 980a30ea6f7847b8b2b82ea8c92ba00acf82cb8dc6c1945225958b8d16d1309b /exec failed with exit code 5
• pull / unittest / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 5
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t deed50f4ee3f2eef949b99abeadc2fdedf671e248f7dc2635d7800bc956fd361 /exec failed with exit code 128
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t ef5d14e265f9d9db250246a4ebbfec39d308d044654aca57c732b71490ff115f /exec failed with exit code 128
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 4ea7edfa0d34ac55aeb72e11c849e0490276a6aa5187175158f8af8105e2ecfa /exec failed with exit code 5
• pull / unittest-editable / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 5
• trunk / unittest-release / macos / macos-job (gh)
  The process '/usr/bin/git' failed with exit code 1

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• trunk / test-arm-cortex-m-size-test (bare_metal) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 1
• trunk / test-arm-cortex-m-size-test (zephyr-preset) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 1
• trunk / unittest-release / linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  The process '/usr/bin/git' failed with exit code 1

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[cccclai]

Makes sense

[swolchok]

failing builds all seem to be failing in HUD as well. merging!