Reduce overlay dependencies on global.h (8) (#2478)

* move variables into z64environment.h

* z_room.h

* z64sram.h, z64ss_sram.h, z64font.h, kanread.h

* z64lifemeter.h, z64debug.h, debug_arena.h

* buffers.h

* remove z_bgcheck global

* gamealloc.h

* suggestions

* .bdd

src/code/graph.c

@@ -1,6 +1,7 @@
 #include "libc64/malloc.h"
 #include "libc64/sprintf.h"
 #include "libu64/debug.h"
+#include "buffers.h"
 #include "gfx.h"
 #include "fault.h"
 #include "line_numbers.h"