feat: abstract I/O and strings for freestanding compilation

Co-authored-by: aider (openrouter/moonshotai/kimi-k2.6) <aider@aider.chat>

Makefile

@@ -1,19 +1,22 @@
-CC = gcc
-CFLAGS = -Wall -Wextra -g -std=c11 -D_POSIX_C_SOURCE=200809L
-LDFLAGS =
-SRCS = forth_core.c forth_dict.c forth_words.c forth_interp.c main.c
-OBJS = $(SRCS:.c=.o)
+CC = clang
+CFLAGS = -Wall -Wextra -g -std=c11
+COMMON_SRCS = forth_core.c forth_dict.c forth_words.c forth_interp.c main.c
+
+HOSTED_SRCS = $(COMMON_SRCS) platform_hosted.c
+FREESTANDING_SRCS = $(COMMON_SRCS) platform_freestanding.c
+
 TARGET = forth
+FREESTANDING_TARGET = forth_freestanding
 
 all: $(TARGET)
 
-$(TARGET): $(OBJS)
-	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+$(TARGET): $(HOSTED_SRCS) forth.h
+	$(CC) $(CFLAGS) -D_POSIX_C_SOURCE=200809L -o $@ $(HOSTED_SRCS)
 
-%.o: %.c forth.h
-	$(CC) $(CFLAGS) -c $< -o $@
+$(FREESTANDING_TARGET): $(FREESTANDING_SRCS) forth.h
+	$(CC) $(CFLAGS) -ffreestanding -nostdlib -fno-stack-protector -o $@ $(FREESTANDING_SRCS)
 
 clean:
-	rm -f $(OBJS) $(TARGET)
+	rm -f $(TARGET) $(FREESTANDING_TARGET)
 
 .PHONY: all clean