chore: Builds now work with Windows Subsystem for Linux (WSL). (#17513)

Small changes to make builds work in Windows Subsystem for Linux (WSL). Verified by **partial** building in Windows 10 + Ubuntu 18.04 WSL.

fixes #55
----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: Litee

tools/@aws-cdk/eslint-plugin/lib/rules/invalid-cfn-imports.ts

@@ -127,7 +127,7 @@ function checkIfImportedLocationIsAnAlphaPackage(location: string, currentFilena
 }
 
 function getCdkRootDir(filename: string): string | undefined {
-  const filenameSplit = filename.split('/');
+  const filenameSplit = filename.split(path.sep);
   // for test files
   let rootDirIndex = filenameSplit.findIndex(e => e.match('tools'));
 

tools/@aws-cdk/pkglint/lib/rules.ts

@@ -130,7 +130,9 @@ export class RepositoryCorrect extends ValidationRule {
     expectJSON(this.name, pkg, 'repository.type', 'git');
     expectJSON(this.name, pkg, 'repository.url', 'https://github.com/aws/aws-cdk.git');
     const pkgDir = path.relative(monoRepoRoot(), pkg.packageRoot);
-    expectJSON(this.name, pkg, 'repository.directory', pkgDir);
+    // Enforcing '/' separator for builds to work in Windows.
+    const osPkgDir = pkgDir.split(path.sep).join('/');
+    expectJSON(this.name, pkg, 'repository.directory', osPkgDir);
   }
 }