build: add CMake option for disabling symbol visibility attributes

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

CMakeLists.txt

@@ -42,6 +42,8 @@ endif()
 
 option(SECP256K1_INSTALL "Enable installation." ${PROJECT_IS_TOP_LEVEL})
 
+option(SECP256K1_ENABLE_API_VISIBILITY_ATTRIBUTES "Enable visibility attributes in the API." ON)
+
 ## Modules
 
 # We declare all options before processing them, to make sure we can express
@@ -312,6 +314,7 @@ else()
   set(cross_status "FALSE")
 endif()
 message("Cross compiling ....................... ${cross_status}")
+message("API visibility attributes ............. ${SECP256K1_ENABLE_API_VISIBILITY_ATTRIBUTES}")
 message("Valgrind .............................. ${SECP256K1_VALGRIND}")
 get_directory_property(definitions COMPILE_DEFINITIONS)
 string(REPLACE ";" " " definitions "${definitions}")

src/CMakeLists.txt

@@ -54,6 +54,10 @@ add_library(secp256k1_precomputed OBJECT EXCLUDE_FROM_ALL
 # from being exported.
 target_sources(secp256k1 PRIVATE secp256k1.c $<TARGET_OBJECTS:secp256k1_precomputed>)
 
+if(NOT SECP256K1_ENABLE_API_VISIBILITY_ATTRIBUTES)
+  target_compile_definitions(secp256k1 PRIVATE SECP256K1_NO_API_VISIBILITY_ATTRIBUTES)
+endif()
+
 # Create a helper lib that parent projects can use to link secp256k1 into a
 # static lib.
 add_library(secp256k1_objs INTERFACE)