[libtins] Fix usage

[JackBoosY]

Fix definiton TINS_API value.

#if defined(_WIN32) && !defined(TINS_STATIC)
    // Export/import symbols, depending on whether we're compiling or consuming the lib
    #ifdef tins_EXPORTS
        #define TINS_API __declspec(dllexport)
    #else
        #define TINS_API __declspec(dllimport)
    #endif // tins_EXPORTS
#else 
    // Otherwise, default this to an empty macro
    #define TINS_API
#endif // _WIN32 && !TINS_STATIC

Fixes #11904.

[ras0219-msft]

LGTM, thanks!