macos: Fix code signing again

As with `otool`, `strip` will also invalidate any code signatures in a
modified binary. So we need to make sure that we invoke `strip` first,
*before* the `cp-with-libs` script is invoked that fixes the code
signatures.

pkg/macos/GNUmakefile

@@ -47,8 +47,9 @@ $(STAGING_DIR): app.icns
 	cp $(TOPLEVEL)/COPYING.md "$(STAGING_DIR)/Software License"
 	ln -s /Applications "$(STAGING_DIR)"
 
-	./cp-with-libs $(TOPLEVEL)/src/sopwith "$(APP_BIN_DIR)"
-	$(STRIP) "$(APP_BIN_DIR)/sopwith"
+	cp "$(TOPLEVEL)/src/sopwith" .
+	$(STRIP) sopwith
+	./cp-with-libs sopwith "$(APP_BIN_DIR)"
 
 	mkdir -p "$(DOC_DIR)"
 	for d in $(DOC_FILES); do \