Fix Makefile flags for autosplitter compilation

Makefile

@@ -4,20 +4,19 @@
 CFLAGS := -Wall -Werror $(shell pkg-config --cflags vtk) -D_POSIX_C_SOURCE=200809L
 LDFLAGS := $(shell pkg-config --libs vtk) -lpthread
 
+SPLITTER_FLAGS := -D_POSIX_C_SOURCE=200809L
+
 HDRS := $(wildcard *.h)
 
 all: adrift splitters
 
 clean:
-	rm -f adrift *.o splitters/*.o splitters/sar_split
+	rm -f adrift *.o splitters/sar_split
 
 splitters: splitters/sar_split
 
 adrift: main.o draw.o common.o io.o calc.o timer.o config.o
 	$(CC) -o $@ $^ $(LDFLAGS)
 
-splitters/sar_split: splitters/sar_split.o
-	$(CC) -o $@ $^ $(LDFLAGS)
-
-%.o: %.c $(HDRS)
-	$(CC) -c -o $@ $< $(CFLAGS)
+splitters/%: splitters/%.c
+	$(CC) -o $@ $^ $(SPLITTER_FLAGS)