cmake: Inherit WERROR setting for secp256k1 build #33297

1. 
   jmoik commented at 6:34 pm on September 3, 2025: none

   This change prevents unexpected CLI output when compiling with -DWERROR=ON (treat warnings as errors). This setting is now properly propagated to the secp256k1 subproject build. Previously, secp256k1 would be built without the -Werror flag even when the main project was configured to treat warnings as errors, creating inconsistent build behavior. https://github.com/bitcoin/bitcoin/issues/33284
2. cmake: Inherit WERROR setting for secp256k1 build ed1c975100
3. DrahtBot added the label Build system on Sep 3, 2025
4. 
   DrahtBot commented at 6:34 pm on September 3, 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/33297.

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   Concept NACK	purpleKarrot

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5. 
   purpleKarrot commented at 9:25 am on September 4, 2025: contributor

   I am going to NACK every PR that adds even more -Werror. 30f642952cb5bf39479bdbe467b3950f0d09324a was a mistake and should be reverted. The correct approach to this is CMAKE_COMPILE_WARNING_AS_ERROR.

   Yes, that requires CMake 3.24 and we allow 3.22 as the minimum. It does not matter. Just accept that the setting will have no effect on Ubuntu 22.04. :man_shrugging:

   cc @hebasto

6. 
   hebasto commented at 11:27 am on September 4, 2025: member

   30f6429 was a mistake…

   Here is some historical context.

   When migrating the build system from Autotools to CMake, there was a unanimous expectation that, at least initially, we should aim for 100% build option compatibility. That commit introduced CMake’s counterpart to Autotools’ --enable-werror:https://github.com/bitcoin/bitcoin/blob/6e62b705328f4a52875a1dd3bfb63fbba8586a01/configure.ac#L284-L289

7. 
   hebasto commented at 11:34 am on September 4, 2025: member

   Yes, that requires CMake 3.24 and we allow 3.22 as the minimum. It does not matter. Just accept that the setting will have no effect on Ubuntu 22.04. 🤷‍♂️

   That seems acceptable to me, as none of the CI jobs use CMake older that 3.24. And when someone sets CMAKE_COMPILE_WARNING_AS_ERROR with an older CMake, it issues a warning:

   0CMake Warning:
   1  Manually-specified variables were not used by the project:
   2
   3    CMAKE_COMPILE_WARNING_AS_ERROR
   

8. 
   purpleKarrot commented at 2:05 pm on September 4, 2025: contributor

   Here is some historical context.

   Don’t take it personal. You did a great job migrating from autotools to CMake. I have zero doubts about that.

Contributors
jmoik DrahtBot purpleKarrot hebasto

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