192 compile warnings in fc/secp256k1

[linh2931]

fc/secp256k1 has 192 compile warnings. They are in the form of

libraries/fc/secp256k1/secp256k1/src/field.h:44:13: warning: ‘secp256k1_fe_normalize’ declared ‘static’ but never defined [-Wunused-function]
libraries/fc/secp256k1/secp256k1/src/field.h:47:13: warning: ‘secp256k1_fe_normalize_weak’ declared ‘static’ but never defined [-Wunused-function]
...
libraries/fc/secp256k1/secp256k1/src/ecmult_impl.h:395:12: warning: ‘secp256k1_ecmult_strauss_batch_single’ defined but not used [-Wunused-function]

They should be cleaned up after the decision of de-submoduling is made.

[spoonincode]

I don't think we've considered desubmoduling this library since we use it verbatim without any modifications.

But the good thing is, we completely control compilation of this library since we use our own CMakeLists.txt (https://github.com/AntelopeIO/fc/blob/main/secp256k1/CMakeLists.txt), so it's trivial to add a -Wnounused-function option here and/or consider these SYSTEM headers.

[stephenpdeos]

Blocked by Desubmodularize fc#122