Well, the good news is I got it to build. The bad news is that it doesn't actually run, just gives the message "EGL Error: Unable to get display!" if run from the command line or "Unable to create EGL display." if run from an xterm.
EDIT: Some of this was wrong for the current Rasbian distro and PPSSPP version. See my updates post further down-thread for updated build instructions.
EDIT: Some of this was wrong for the current Rasbian distro and PPSSPP version. See my updates post further down-thread for updated build instructions.

