macros.txt: list all predefined macros

Makefile

@@ -13,7 +13,7 @@ TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs \
 				positional-format-strings
 EXTRAS=mandelbrot.bmp multibrot.png test-inline-assembly.s \
 				mtrace-test.trace mtrace-test.txt multibrot-openmp.png
-VERYEXTRAS=cppcheck.txt tags
+VERYEXTRAS=cppcheck.txt macros.txt tags
 
 .PHONY: all
 all: $(TARGETS)
@@ -88,3 +88,6 @@ multibrot-openmp: multibrot-openmp.c
 
 mandelbrot-openmp: mandelbrot-openmp.c
 	$(CC_OPENMP) $(CFLAGS_OPENMP) $(shell sdl-config --cflags) -o $@ $< $(shell sdl-config --libs) -lm
+
+macros.txt:
+	$(CC) -dM -E -x c /dev/null > $@