It looks like the calling convention and return type change between the .h and the .cpp, for whatever reason.
Example error:
Error C2440 ‘initializing’: cannot convert from ‘GLenum (__stdcall *)(void)’ to ‘GLenum (__cdecl *const &)(void)’ (compiling source file …..\JuceLibraryCode\include_juce_opengl.cpp) Audome_SharedCode 4045 (My Project)\JUCE\modules\juce_opengl\opengl\juce_gl.cpp