Build secp256k1 via cmake ExternalProject, no pre-built DLL required.

[danrmiller]

Resolves the TODO in windows/CMakeLists.txt, so re-enables add_subdirectory in src/CMakeLists.txt so secp256k1 is built via cmake ExternalProject during flutter build windows, the same way it works on Linux and Android. No pre-built DLL required.

Tested on windows-latest (Windows Server 2025, VS 2026): https://github.com/cypherstack/coinlib/actions/runs/26660965448/job/78583115194

[MatthewLM]

Thank you @danrmiller. Sorry for the delay in getting to this.

secp256k1 builds are now moving to use https://github.com/peercoin/secp256k1-coinlib in branch v5.0.0.

Would you be willing to get this to work for v5.0.0 and verify that the coinlib/bin build scripts for windows also work?

Otherwise Windows support will be dropped for v5.0.0 unless someone else can test.

[sneurlax]

Thank you @danrmiller. Sorry for the delay in getting to this.

secp256k1 builds are now moving to use https://github.com/peercoin/secp256k1-coinlib in branch v5.0.0.

Would you be willing to get this to work for v5.0.0 and verify that the coinlib/bin build scripts for windows also work?

Otherwise Windows support will be dropped for v5.0.0 unless someone else can test.

Hey @MatthewLM, I will check this tomorrow. I only just saw it or else I'd have done it earlier. Been working on Windows today, guess I will be tomorrow as well :)