Create a cmake function to test for conflicting flags

[jathu]

Summary

We currently have some flags that cannot be turned on with other flags. We currently work around this be implicitly flipping the other flags. Let's make this violation explicit now and expect the users to exclude the conflicting flag.

Example:

executorch/CMakeLists.txt

Lines 550 to 563 in b632906

	if(EXECUTORCH_BUILD_DEVTOOLS)
	if(NOT EXECUTORCH_BUILD_ARM_BAREMETAL)
	set(EXECUTORCH_BUILD_EXTENSION_DATA_LOADER
	ON
	CACHE BOOL "EXECUTORCH_BUILD_EXTENSION_DATA_LOADER" FORCE
	)
	else()
	set(EXECUTORCH_BUILD_EXTENSION_DATA_LOADER
	OFF
	CACHE BOOL "EXECUTORCH_BUILD_EXTENSION_DATA_LOADER" FORCE
	)
	endif()
	add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/devtools)
	endif()

Test plan

$ python -m unittest tools.cmake.common.preset_test.TestPreset

cc @larryliu0820

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/11460

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⏳ 88 Pending, 1 Unrelated Failure

As of commit cbafa43 with merge base b632906 ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-llama_runner_eager-linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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