Rearrange Makefile to better organize components

Makefile

@@ -1,7 +1,9 @@
 #CROSS_COMPILE = arm-none-eabi-
-OS = linux
+SYS = linux
 GFX = sdl
 
+NESE_DEBUG = CART
+
 CC = $(CROSS_COMPILE)gcc
 LD = $(CC)
 #CFLAGS = -mcpu=cortex-m33 -mthumb
@@ -28,19 +30,20 @@ TEST_OBJS = $(TEST_SRCS:%.c=$(OBJDIR)/%.o)
 
 MAPDIR = $(SRCDIR)/map
 GFXDIR = $(SRCDIR)/$(GFX)
+SYSDIR = $(SRCDIR)/$(SYS)
 
-NESE_SRC_SRCS = f6502.c f6502_opcodes.c
-NESE_SRC_SRCS += nese.c nes.c cart.c mapper.c
-NESE_SRC_SRCS += ppu.c apu.c
-NESE_SRC_SRCS += memory.c serdes.c save.c rle.c cartinfo.c
-NESE_SRC_SRCS += menu.c list.c state.c menus.c
-NESE_SRC_SRCS += $(OS)/port.c
+NESE_SYS_SRCS = $(notdir $(wildcard $(SYSDIR)/*.c))
 NESE_GFX_SRCS = $(notdir $(wildcard $(GFXDIR)/*.c))
 NESE_MAP_SRCS = $(notdir $(wildcard $(MAPDIR)/*.c))
 
-NESE_DEBUG = CART
+NESE_SRC_SRCS = f6502.c f6502_opcodes.c
+NESE_SRC_SRCS += nese.c nes.c cart.c mapper.c
+NESE_SRC_SRCS += memory.c ppu.c apu.c
+NESE_SRC_SRCS += serdes.c save.c rle.c cartinfo.c
+NESE_SRC_SRCS += menu.c list.c state.c menus.c
 
 NESE_SRCS += $(NESE_SRC_SRCS:%=$(SRCDIR)/%)
+NESE_SRCS += $(NESE_SYS_SRCS:%=$(SYSDIR)/%)
 NESE_SRCS += $(NESE_MAP_SRCS:%=$(MAPDIR)/%)
 NESE_SRCS += $(NESE_GFX_SRCS:%=$(GFXDIR)/%)
 NESE_OBJS = $(NESE_SRCS:%.c=$(OBJDIR)/%.o)