cmake: exclude secp256k1 from all #33390

Instead of setting the EXCLUDE_FROM_ALL target property, pass EXCLUDE_FROM_ALL to add_subdirectory().

This has the following advanteges:

• It is shorter (obviously).
• Target properties are set only in the CMakeLists.txt file that defines the target.
• Install rules defined in the subdirectory are excluded as well. This is what we want, because secp256k1 is linked statically.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33390.

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Reviews

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Conflicts

No conflicts as of last run.

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CI fails:

The following tests FAILED:
	  4 - secp256k1_noverify_tests (Not Run)
	  5 - secp256k1_tests (Not Run)
	  6 - secp256k1_exhaustive_tests (Not Run)
Errors while running CTest

Could turn into draft while CI is red?

Are you still working on this?

This has been in draft for 5 months, and the CI has never been passing, so closing for now. Feel free to comment if you want this reopened.