More Makefile fixes

Makefile

@@ -1,34 +1,29 @@
 .PHONY: clean lib client server passwd
 
+SUBDIRS = hkexpasswd hkexsh hkexshd
+
 all: lib client server passwd
 
 clean:
-	rm -f\
- hkexsh/hkexsh hkexsh/hkexsh.exe\
- hkexshd/hkexshd hkexshd/hkexshd.exe\
- hkexpasswd/hkexpasswd hkexpasswd/hkexpasswd.exe
-
+	go clean .
+	for d in $(SUBDIRS); do\
+	  $(MAKE) -C $$d clean;\
+	done
 
 lib:
 	go install .
 
 client: lib
-	@cd hkexsh
-	go build .
-	@cd -
+	$(MAKE) -C hkexsh
 
 ifneq ($(MSYSTEM),)
 server: lib
-	@echo "hkexshd server not supported on Windows (yet)"
+	echo "hkexshd server not supported on Windows (yet)"
 else
 server: lib
-	@cd hkexshd
-	go build .
-	@cd -
+	$(MAKE) -C hkexshd
 endif
 
 passwd: lib
-	@cd hkexpasswd
-	@go build .
-	@cd -
+	$(MAKE) -C hkexpasswd