Proper support for BUILD_SHARED_LIBS on Windows

[aschet]

Describe the feature or improvement you're requesting

It would be great if you could add proper support for the compilation of the library as DLL on Windows via the BUILD_SHARED_LIBS CMake variable. Currently the __declspec(dllexport) attribute is applied to many methods in the codebase. If there is no intention to support DLL compilation, please remove the __declspec(dllexport) attribute since it is not required for static libraries. I would even consider this an error as it is applied now. To support DLL compilation, something like this has to be implemented:

liboai\include\core\response.h:

#if defined(__linux__) || defined(__APPLE__)
	#define LIBOAI_EXPORT
#else
	#ifdef LIBOAI_DLL
		#ifdef LIBOAI_BUILD
			#define LIBOAI_EXPORT __declspec(dllexport)
		#else
			#define LIBOAI_EXPORT __declspec(dllimport)
		#endif
	#else
		#define LIBOAI_EXPORT
	#endif
#endif

liboai\CMakeLists.txt:

if(BUILD_SHARED_LIBS)
  target_compile_definitions(${PROJECT_NAME}
    PRIVATE
      LIBOAI_BUILD
    PUBLIC
      LIBOAI_DLL
  )
endif()

Furthermore, the LIBOAI_EXPORT macro has to be applied to all methods that are used by a client.

Additional context

No response

[richinseattle]

I'm not sure if this fixes your specific issue, but after fixing the MSVC/vcpkg build configuration in #84 I tried

cmake .. -DBUILD_SHARED_LIBS:BOOL=ON

and was able to build DLLs. There may be some extra exports there, but its usable.

[aschet]

I'm not sure if this fixes your specific issue, but after fixing the MSVC/vcpkg build configuration in #84

Unfortunately, it doesn't. Also, if you compile with the -DBUILD_EXAMPLES:BOOL=ON option in addition to -DBUILD_SHARED_LIBS:BOOL=ON, you will get multiple linker errors due to missing exports. Since with #84 find_package is only done for WIN32, will this not interfere with the build on other platforms?