Update CHANGELOG.md

Co-authored-by: Tim Ruffing <dev@real-or-random.org>

Author: jonasnick

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 #### Added
  - CMake: Added `secp256k1_objs` interface library to allow parent projects to embed libsecp256k1 object files into their own static libraries.
+ - build: Added `SECP256K1_NO_API_VISIBILITY_ATTRIBUTES` preprocessor flag (CMake option: `SECP256K1_ENABLE_API_VISIBILITY_ATTRIBUTES`) that disables explicit "visibility" attributes for API symbols. Defining this macro enables the user to control the visibility of the API symbols via `-fvisibility=<value>` when building libsecp256k1. (All non-API declarations will always have hidden visibility, even with `SECP256K1_ENABLE_API_VISIBILITY_ATTRIBUTES` defined.) For instance, `-fvisibility=hidden` can be useful even for the API symbols, e.g., when building a static libsecp256k1 which is linked into a shared library, and the latter should not re-export the libsecp256k1 API.
 
 #### Changed
  - The pointers `secp256k1_context_static` and `secp256k1_context_no_precomp` to the constant context object are now const.