Always set __declspec(dllexport) for classes

[bugdea1er]

Apparently you can always specify dllexport for library classes on Windows, so this pull request eliminates the need to add the TMP_BUILDING_DLL compilation definition

[Copilot]

Pull Request Overview

This PR simplifies the ABI definition for Windows by always exporting library classes with __declspec(dllexport), removing the conditional TMP_BUILDING_DLL logic.

• Removes the TMP_BUILDING_DLL condition for Windows builds
• Unconditionally defines abi as __declspec(dllexport) on Windows
• Retains the default visibility attribute for non-Windows platforms

Files not reviewed (2)

• meson.build: Language not supported
• src/CMakeLists.txt: Language not supported

Comments suppressed due to low confidence (1)

src/abi.hpp:4

• Removing the TMP_BUILDING_DLL check results in using __declspec(dllexport) unconditionally on Windows. Please verify that this change does not lead to linking issues when importing the library.

#if defined TMP_BUILDING_DLL