starpupy: Generalize getting python include flag

starpupy/wrapper/starpu/Makefile

@@ -1,4 +1,6 @@
-CPPFLAGS=-I/usr/include/python3.6 -Wall -O2 -g
+PYTHON ?= python3.6
+
+CPPFLAGS = $(shell $(PYTHON)-config --includes) -Wall -O2 -g
 CFLAGS += $(shell pkg-config --cflags starpu-1.3)
 LDLIBS += $(shell pkg-config --libs starpu-1.3)
 
@@ -8,4 +10,4 @@ task.so: starpu_task_wrapper.c Makefile
 	$(CC) -fPIC $(CFLAGS) $< -o $@ -shared  $(CPPFLAGS) $(LDLIBS)
 
 clean:
-	rm -f task.so
+	rm -f task.so