wasm2c: update Windows build to always use internal sha256 library to resolve libcrypto DLL not found issue

[silbinarywolf]

Fixes #2609

[keithw]

I don't use Windows myself, but I think this libcrypto stuff has been causing us enough trouble (on platforms that are maybe not as strong at versioning/managing dependencies) that we should probably just switch to an always-vendored BLAKE3 hash for this and ditch the external library. I'll send a PR on this.