GLupeN64 is mupen64plus + GLideN64 + libretro.

How is this different from mupen64plus-libretro?

mupen64plus-libretro implements multiple Graphics plugins. There are also
code modifications that make it different than standalone mupen64plus.

GLupeN64 uses GLideN64 (a graphics plugin that is not available in
mupen64plus-libretro). The emulator code itself is identical to
standalone mupen64plus.

By choosing one graphics plugin (GLideN64), we will be able to keep the
code in line with upstream, and maintaining the code will be much simpler.

To build the debugging symbols use:
  DEBUG=1 ./GLupeN64.SlackBuild