native make: prevent redundant include dir copy

com.oracle.truffle.r.native/run/Makefile

@@ -84,7 +84,9 @@ $(FASTR_BIN_DIR)/R: Makefile R.sh Rscript.sh Rscript_exec.sh
 	# overrides
 	cp examples-header.R examples-footer.R $(FASTR_SHARE_DIR)/R
 
-includedir: Makefile $(TOPDIR)/include/Rinternals.h
+includedir: $(FASTR_R_HOME)/include/Rinternals.h
+
+$(FASTR_R_HOME)/include/Rinternals.h: Makefile $(TOPDIR)/include/Rinternals.h
 	mkdir -p $(FASTR_R_HOME)/include
 	cp -r $(TOPDIR)/include/* $(FASTR_R_HOME)/include