cmake: Proactively avoid use of SECP256K1_DISABLE_SHARED #33101

1. 
   hebasto commented at 12:48 pm on July 30, 2025: member

   The SECP256K1_DISABLE_SHARED CMake variable has been removed upstream.

   This PR removes its usage ahead of the next secp256k1 subtree update to prevent breakage and simplify integration.

2. cmake, refactor: Encapsulate adding secp256k1 subtree in function 14b2dd3265
3. cmake: Proactively avoid use of `SECP256K1_DISABLE_SHARED`

   The `SECP256K1_DISABLE_SHARED` CMake variable has been removed upstream.
   
   This change removes its usage ahead of the next `secp256k1` subtree
   update to prevent breakage and simplify integration.

   d5d95035bc
4. hebasto added the label Build system on Jul 30, 2025
5. 
   DrahtBot commented at 12:48 pm on July 30, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33101.

   Reviews

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   Type	Reviewers
   ACK	theuni

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   Conflicts

   Reviewers, this pull request conflicts with the following ones:

   • #32724 (Musig2 tests by w0xlt)
   • #32617 ([Draft/POC] Add secp256k1-based HPKE (Hybrid Public Key Encryption) For Payjoin v2 by w0xlt)
   • #32367 (cmake: Check user-defined APPEND_*FLAGS variables early by hebasto)
   • #31244 (descriptors: MuSig2 by achow101)
   • #29675 (wallet: Be able to receive and spend inputs involving MuSig2 aggregate keys by achow101)
   • #29491 ([EXPERIMENTAL] Schnorr batch verification for blocks by fjahr)

   If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

6. 
   fanquake commented at 3:52 pm on July 30, 2025: member

   cc @theuni @purpleKarrot
7. theuni approved
8. 
   theuni commented at 6:33 pm on July 30, 2025: member

   Nice. I’ve been wanting to scope the secp add_subdirectory for a while now.

   utACK d5d95035bc6ef135476d7f734c574b38d6faaf70. Reviewed with git diff --color-moved=dimmed-zebra --color-moved-ws=allow-indentation-change

9. DrahtBot added the label Needs rebase on Jul 31, 2025
10. 
    DrahtBot commented at 10:36 pm on July 31, 2025: contributor

    🐙 This pull request conflicts with the target branch and needs rebase.

Contributors
hebasto DrahtBot fanquake theuni

Labels
Build system Needs rebase