Add preprocessing step

Makefile

@@ -0,0 +1,43 @@
+CC = arm-none-eabi-gcc
+
+CFLAGS = -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16
+CFLAGS += -Wall -Werror -Wpedantic -Wextra
+# Remove unused code and data; https://gcc.gnu.org/onlinedocs/gnat_ugn/Compilation-options.html
+CFLAGS += -ffunction-sections -fdata-sections
+# Don't include memcpy
+CFLAGS += -fno-builtin
+# "-fno-common ... specifies that the compiler places uninitialized global variables in the BSS section of the object file."
+CFLAGS += -fno-common
+
+DEBUG ?= 1
+ifeq ($(DEBUG), 0)
+	# Optimize for size
+	CFLAGS += -Os
+else
+	CFLAGS += -O0 -g3 -ggdb
+endif
+
+LDFLAGS = -T link.ld -nostartfiles -nostdlib --specs nano.specs -lc -lgcc -Wl,--gc-sections -Wl,-Map=$@.map
+
+SRC_DIR = src
+BUILD_DIR = build
+
+SRC_FILES := $(wildcard $(SRC_DIR)/*.c)
+PREP_FILES := $(patsubst $(SRC_DIR)/%.c,$(BUILD_DIR)/%.i,$(SRC_FILES))
+
+.PHONY: build
+build: builddir preprocess
+
+$(BUILD_DIR)/%.i: $(SRC_DIR)/%.c
+	$(CC) $(CFLAGS) -E $^ -o $@
+
+.PHONY: builddir
+builddir:
+	mkdir $(BUILD_DIR)
+
+.PHONY: preprocess
+preprocess: $(PREP_FILES)
+
+.PHONY: clean
+clean:
+	rm -rf $(BUILD_DIR)