Cannot build on Linux

Following the instructions on https://docs.libretro.com/development/retroarch/compilation/linux-and-bsd/ results in being unable to compile bsnes balanced (or more precisely, being unable to compile it with openGL).

Adding $(info statements to the Makefile to trace through it and find the problem shows me that the platform is set to "unix-opengl" and the Makefile does not understand that, causing it to fall through to the else statement that applies to Windows. It then tries to compile a .dll using Windows libraries, which fails.

In addition, the libretro-build.sh script doesn't properly report the error. What actually happens is that bsnes is compiled twice, once successfully (as unix) and once unsuccessfully (as unix-opengl). However, the summary at the end of the script just says that the core was not processed successfully, rather than saying that it was successfully processed one way and unsuccessfully another.

Read the Linux compilation instructions, then inspect the Makefile platform branches and libretro-build.sh. Reproduce the bsnes balanced OpenGL build and trace the unix-opengl path; done means it no longer selects Windows libraries and the script summary distinguishes successful and failed processing attempts.