fixes for compiling with gcc 10

gcc 10 no longer lets you get away with not externing global variables in header files. This adds the necessary extern and adds defines in appropriate c files

bootloader/storage/emummc.h

@@ -47,7 +47,7 @@ typedef struct _emummc_cfg_t
 	int fs_ver;
 } emummc_cfg_t;
 
-emummc_cfg_t emu_cfg;
+extern emummc_cfg_t emu_cfg;
 
 void emummc_load_cfg();
 bool emummc_set_path(char *path);