Actually fix parallel builds

Author: sfackler

Makefile.in

@@ -16,13 +16,13 @@ OPENSSL_STAMP := $(BUILDDIR)/openssl.stamp
 
 $(PHF): $(PHF_STAMP)
 
-$(PHF_STAMP):
+$(PHF_STAMP): | $(BUILDDIR)
 	$(MAKE) -C $(PHF_DIR)
 	touch $(PHF_STAMP)
 
 $(OPENSSL): $(OPENSSL_STAMP)
 
-$(OPENSSL_STAMP):
+$(OPENSSL_STAMP): | $(BUILDDIR)
 	$(MAKE) -C $(OPENSSL_DIR)
 	touch $(OPENSSL_STAMP)