带'='的OpenGL活动纹理重定义错误：作为左操作数的函数

Question

我正在尝试在Visual Studio 2015中构建开源项目nanogui-sdl。

添加所有必需的库后，我收到以下两个错误：

Error C2365 - 'glActiveTexture': redefinition; previous definition was 'function'
Error C2659 - '=': function as left operand

以下是令人讨厌的代码行：

#ifdef WIN32
    PFNGLACTIVETEXTUREPROC glActiveTexture;
#else

...

#ifdef WIN32
    ASSIGNGLFUNCTION(PFNGLACTIVETEXTUREPROC,glActiveTexture)
#endif