fix prebuilt on windows, using vendored ninja

Author: bobzhang

scripts/prebuilt.js

@@ -4,7 +4,7 @@ var path = require("path");
 var { sys_extension, is_windows } = require("./config.js");
 
 var root = path.join(__dirname, "..");
-var root_config = { cwd: root, stdio: [0, 1, 2] };
+var root_config = { cwd: root, stdio: [0, 1, 2], encoding: 'utf8' };
 process.env.BS_RELEASE_BUILD = "true";
 
 var ocamlVersion = require("./buildocaml.js").getVersionPrefix();
@@ -41,8 +41,11 @@ function buildCompiler() {
   });
 
   fs.writeFileSync(path.join(root, "lib", prebuilt), content, "ascii");
+  process.env.PATH=
+    `${path.join(__dirname,'..','vendor','ninja','snapshot')}${path.delimiter}${process.env.PATH}`
+  let ninjaPath = `ninja${sys_extension}`
   cp.execSync(
-    `ninja -C lib -f ${prebuilt} -t clean && ninja -C lib -f ${prebuilt}`,
+    `${ninjaPath} -C lib -f ${prebuilt} -t clean && ${ninjaPath} -C lib -f ${prebuilt}`,
     root_config
   );
 }