fix(compiler): properly work on windows

Verified manually on a windows surface tablet.

Fixes #19492

packages/compiler-cli/src/transformers/compiler_host.ts

@@ -108,7 +108,8 @@ export class TsCompilerAotCompilerTypeCheckHostAdapter extends
   private resolveModuleName(moduleName: string, containingFile: string): ts.ResolvedModule
       |undefined {
     const rm = ts.resolveModuleName(
-                     moduleName, containingFile, this.options, this, this.moduleResolutionCache)
+                     moduleName, containingFile.replace(/\\/g, '/'), this.options, this,
+                     this.moduleResolutionCache)
                    .resolvedModule;
     if (rm && this.isSourceFile(rm.resolvedFileName)) {
       // Case: generateCodeForLibraries = true and moduleName is

packages/compiler-cli/test/transformers/compiler_host_spec.ts

@@ -41,16 +41,18 @@ describe('NgCompilerHost', () => {
       basePath: '/tmp',
       moduleResolution: ts.ModuleResolutionKind.NodeJs,
     },
+    rootNames = ['/tmp/index.ts'],
     ngHost = createNgHost({files}),
     librarySummaries = [],
   }: {
     files?: Directory,
     options?: CompilerOptions,
+    rootNames?: string[],
     ngHost?: CompilerHost,
     librarySummaries?: LibrarySummary[]
   } = {}) {
     return new TsCompilerAotCompilerTypeCheckHostAdapter(
-        ['/tmp/index.ts'], options, ngHost, new MetadataCollector(), codeGenerator,
+        rootNames, options, ngHost, new MetadataCollector(), codeGenerator,
         new Map(librarySummaries.map(entry => [entry.fileName, entry] as[string, LibrarySummary])));
   }
 
@@ -143,6 +145,15 @@ describe('NgCompilerHost', () => {
       const host = createHost({ngHost});
       expect(host.moduleNameToFileName('a', 'b')).toBe('someResult');
     });
+
+    it('should work well with windows paths', () => {
+      const host = createHost({
+        rootNames: ['\\tmp\\index.ts'],
+        options: {basePath: '\\tmp'},
+        files: {'tmp': {'node_modules': {'@core': {'index.d.ts': dummyModule}}}}
+      });
+      expect(host.moduleNameToFileName('@core/index')).toBe('/tmp/node_modules/@core/index.d.ts');
+    });
   });
 
   describe('resourceNameToFileName', () => {