Update to v103r21 release.

byuu says:

Changelog:

  - gb: added TAMA emulation [thanks to endrift for the initial notes]
  - gb: save RTC memory to disk (MBC3 doesn't write to said memory yet;
    TAMA doesn't emulate it yet)
  - gb: expect MMM01 boot loader to be at end of ROM instead of start
  - gb: store MBC2 save RAM as 256-bytes (512x4-bit) instead of
    512-bytes (with padding)
  - gb: major cleanups to every cartridge mapper; moved to Mapper class
    instead of MMIO class
  - gb: don't serialize all mapper states with every save state; only
    serialize the active mapper
  - gb: serialize RAM even if a battery isn't present¹
  - gb/cartridge: removed unnecessary code; refactored other code to
    eliminate duplication of functions
  - icarus: improve GB(C) heuristics generation to not include filenames
    for cartridges without battery backup
  - icarus: remove incorrect rearrangement of MMM01 ROM data
  - md/vdp: fix CRAM reads -- fixes Sonic Spinball colors [hex\_usr]
  - tomoko: hide the main higan window when entering fullscreen
    exclusive mode; helps with multi-monitor setups
  - tomoko: destroy ruby drivers before calling Application::quit()
    [Screwtape]
  - libco: add settings.h and defines to fiber, ucontext [Screwtape]

¹: this is one of those crystal clear indications that nobody's
actually playing the higan DMG/CGB cores, or at least not with save
states. This was a major mistake.

Note: I can't find any official documentation that `GL_ALPHA_TEST` was
removed from OpenGL 3.2. Since it's not hurting anything except showing
some warnings in debug mode, I'm just going to leave it there for now.

libco/ucontext.c

@@ -12,8 +12,10 @@
 
 #define LIBCO_C
 #include "libco.h"
+#include "settings.h"
 
 #define _BSD_SOURCE
+#define _XOPEN_SOURCE 500
 #include <stdlib.h>
 #include <ucontext.h>