path: fix posix.relative() on Windows

Fixes: https://github.com/nodejs/node/issues/13683

PR-URL: https://github.com/nodejs/node/pull/37747
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/path.js

@@ -23,11 +23,15 @@
 
 const {
   FunctionPrototypeBind,
+  RegExp,
   StringPrototypeCharCodeAt,
+  StringPrototypeIndexOf,
   StringPrototypeLastIndexOf,
+  StringPrototypeReplace,
   StringPrototypeSlice,
   StringPrototypeToLowerCase,
 } = primordials;
+
 const {
   CHAR_UPPERCASE_A,
   CHAR_LOWERCASE_A,
@@ -1014,7 +1018,17 @@ const posix = {
     let resolvedAbsolute = false;
 
     for (let i = args.length - 1; i >= -1 && !resolvedAbsolute; i--) {
-      const path = i >= 0 ? args[i] : process.cwd();
+      let path;
+      if (i >= 0) {
+        path = args[i];
+      } else {
+        const _ = StringPrototypeReplace(
+          process.cwd(),
+          new RegExp(`\\${module.exports.sep}`, 'g'),
+          posix.sep
+        );
+        path = StringPrototypeSlice(_, StringPrototypeIndexOf(_, posix.sep));
+      }
 
       validateString(path, 'path');