build: Enable -Werror=sign-compare
build: Enable -Werror=sign-compare

Explicitly add -Wsign-compare as well - not required for all compilers, as GCC activates it
under -Wall, but may impact clang, etc.


Former-commit-id: 011564b4578087817ffae7ebcd30f040a640e478
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin