Add simple config system for both #ifdef's and conditional compilation

Makefile

@@ -18,10 +18,13 @@ OBJDUMP = $(TOOL_PREFIX)objdump
 
 # Define the flags we'll need for our tools
 INCLUDES = -I include
-KCFLAGS = -g -Wall -Wextra -Werror -nostdlib -nostartfiles -fno-builtin -std=gnu99 $(INCLUDES)
+KCFLAGS = -g -Wall -Wextra -Werror -nostdlib -nostartfiles -fno-builtin -std=gnu99 -include config.h $(INCLUDES)
 KLDFLAGS = -T link.ld -L /usr/lib/gcc/arm-elf/4.7.0/
 EXTRA_LIBS = -lgcc
 
+# Include the config file so we don't compile/link unnecessary objects
+include config
+
 # Define KOBJS as a 'simply expanded' variable
 KOBJS :=
 
@@ -48,7 +51,7 @@ aedrix-kernel.img: aedrix-kernel.elf
 	@echo 'OBJCOPY   $@'
 	$(V)$(OBJCOPY) $< -O binary $@
 
-%.o: %.c
+%.o: %.c config.h
 	@echo '     CC   $@'
 	$(V)$(CC) $(KCFLAGS) -MD -c -o $@ $<
 	@# Automatic dependency generation fixups (http://mad-scientist.net/make/autodep.html)
@@ -57,7 +60,7 @@ aedrix-kernel.img: aedrix-kernel.elf
 		-e '/^$$/ d' -e 's/$$/ :/' < $*.d >> $(*D)/.$(*F).d; \
 		rm -f $*.d
 
-%.o: %.S
+%.o: %.S config.h
 	@echo '     AS   $@'
 	$(V)$(CC) $(KCFLAGS) -MD -c -o $@ $<
 	@# Automatic dependency generation fixups (http://mad-scientist.net/make/autodep.html)
@@ -66,7 +69,16 @@ aedrix-kernel.img: aedrix-kernel.elf
 		-e '/^$$/ d' -e 's/$$/ :/' < $*.d >> $(*D)/.$(*F).d; \
 		rm -f $*.d
 
+config.h: config
+	@echo ' CONFIG   config.h'
+	@cp config config.h
+	@sed -i '/^\w*#/d' config.h
+	@sed -i '/^\s*\(CONFIG_[A-Z0-9_]\+\)\s*=\s*[nN]/d' config.h
+	@sed -i 's/^\s*\(CONFIG_[A-Z0-9_]\+\)\s*=\s*[yY]/#define \1/g' config.h
+
 clean:
+	@echo '  CLEAN   config.h'
+	$(V)rm -f config.h
 	@echo '  CLEAN   *.o'
 	$(V)rm -f $(KOBJS)
 	@echo '  CLEAN   .*.d'