cmake: Export symbols on windows when building as SHARED lib

CMakeLists.txt

@@ -53,6 +53,10 @@ else()
   endforeach()
 endif()
 
+if(BUILD_SHARED_LIBS AND MSVC)
+  set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
+endif()
+
 # By default only build the C++ library.
 option(BUILD_CXX "Build C++ library" ON)
 message(STATUS "Build C++ library: ${BUILD_CXX}")