The CPU core of the Game Boy is (most likely) called SM83

Core/gb.h

@@ -17,7 +17,7 @@
 #include "printer.h"
 #include "timing.h"
 #include "rewind.h"
-#include "z80_cpu.h"
+#include "sm83_cpu.h"
 #include "symbol_hash.h"
 #include "sgb.h"
 

Core/sm83_cpu.h

@@ -1,5 +1,5 @@
-#ifndef z80_cpu_h
-#define z80_cpu_h
+#ifndef sm83_cpu_h
+#define sm83_cpu_h
 #include "gb_struct_def.h"
 #include <stdint.h>
 
@@ -8,4 +8,4 @@ void GB_cpu_disassemble(GB_gameboy_t *gb, uint16_t pc, uint16_t count);
 void GB_cpu_run(GB_gameboy_t *gb);
 #endif
 
-#endif /* z80_cpu_h */
+#endif /* sm83_cpu_h */

libretro/Makefile.common

@@ -8,7 +8,7 @@ SOURCES_C   := $(CORE_DIR)/Core/gb.c \
                $(CORE_DIR)/Core/display.c \
                $(CORE_DIR)/Core/symbol_hash.c \
                $(CORE_DIR)/Core/camera.c \
-               $(CORE_DIR)/Core/z80_cpu.c \
+               $(CORE_DIR)/Core/sm83_cpu.c \
                $(CORE_DIR)/Core/joypad.c \
                $(CORE_DIR)/Core/save_state.c \
                $(CORE_DIR)/libretro/agb_boot.c \