workarounds for #16819 - TS2.1 compiler issues

src/vs/editor/contrib/snippet/common/snippetParser.ts

@@ -124,7 +124,7 @@ export class Scanner {
 export abstract class Marker {
 	_markerBrand: any;
 
-	static toString(marker: Marker[]): string {
+	static toString(marker?: Marker[]): string {
 		let result = '';
 		for (const m of marker) {
 			result += m.toString();

src/vs/workbench/api/node/extHostConfiguration.ts

@@ -107,6 +107,6 @@ export class ExtHostConfiguration extends ExtHostConfigurationShape {
 			mixin(result, config, false);
 		}
 
-		return Object.freeze(result);
+		return <WorkspaceConfiguration>Object.freeze(result);
 	}
 }

src/vs/workbench/api/node/extHostDiagnostics.ts

@@ -166,7 +166,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 		this._checkDisposed();
 		let result = this._data[uri.toString()];
 		if (Array.isArray(result)) {
-			return Object.freeze(result.slice(0));
+			return <vscode.Diagnostic[]>Object.freeze(result.slice(0));
 		}
 	}