fix #4716 introduce ninja as a submodule

.gitmodules

@@ -5,3 +5,6 @@
 	path = syntax
 	url = https://github.com/rescript-lang/syntax
 	branch = master
+[submodule "ninja"]
+	path = ninja
+	url = git@github.com:rescript-lang/ninja.git

scripts/prebuilt.js

@@ -14,7 +14,7 @@ var hostPlatform = "darwin";
 function rebuild() {
   cp.execSync(`node ${path.join(__dirname, "ninja.js")} cleanbuild`, {
     cwd: __dirname,
-    stdio: [0, 1, 2]
+    stdio: [0, 1, 2],
   });
 }
 
@@ -28,7 +28,7 @@ function buildCompiler() {
       ? `ocamlopt.opt.exe`
       : `../native/${ocamlVersion}/bin/ocamlopt.opt`,
     INCL: ocamlVersion,
-    isWin: is_windows
+    isWin: is_windows,
   });
 
   fs.writeFileSync(path.join(root, "lib", prebuilt), content, "ascii");
@@ -52,12 +52,19 @@ if (!is_windows) {
 function createOCamlTar() {
   if (process.platform === hostPlatform) {
     require("./installUtils.js").install();
+    console.log(`status in ocaml submodule:`)
     cp.execSync(`git -C ocaml status -uno`, { cwd: root, stdio: [0, 1, 2] });
     cp.execSync(
       `git  -C ocaml archive --format=tar.gz HEAD -o ../vendor/ocaml.tar.gz`,
       { cwd: root, stdio: [0, 1, 2] }
     );
   }
+  console.log(`status in ninja submodule:`)
+  cp.execSync(`git -C ninja status -uno`, { cwd: root, stdio: [0, 1, 2] });
+  cp.execSync(
+    `git -C ninja archive --format=tar.gz HEAD -o ../vendor/ninja.tar.gz`,
+    { cwd: root, stdio: [0, 1, 2] }
+  );
 }
 
 createOCamlTar();