Simplify autoreload backend selection in Makefile

Makefile

@@ -21,16 +21,13 @@ ifndef NO_LIBEXIF
 	LIBS     += -lexif
 endif
 
-.PHONY: clean install uninstall
+# select autoreload backend
+# overwritten with `make AUTORELOAD=nop`
+AUTORELOAD := inotify
 
-SRC := commands.c image.c main.c options.c thumbs.c util.c window.c
-# conditionally compile in autoreload-backend; usage: `make AUTORELOAD=nop`
-ifeq ($(AUTORELOAD),nop)
-	SRC += autoreload_nop.c
-else
-	SRC += autoreload_inotify.c
-endif
+.PHONY: clean install uninstall
 
+SRC := autoreload_$(AUTORELOAD).c commands.c image.c main.c options.c thumbs.c util.c window.c
 DEP := $(SRC:.c=.d)
 OBJ := $(SRC:.c=.o)