Create typeof's string literal union type once

This changes the print order of string literal unions slightly. I think
this is because 'string', 'symbol', etc are added to a union very early
on in the creation of the checker.

src/compiler/checker.ts

@@ -326,7 +326,6 @@ namespace ts {
             "object": TypeFacts.TypeofEQObject,
             "function": TypeFacts.TypeofEQFunction
         });
-
         const typeofNEFacts = createMapFromTemplate({
             "string": TypeFacts.TypeofNEString,
             "number": TypeFacts.TypeofNENumber,
@@ -336,7 +335,6 @@ namespace ts {
             "object": TypeFacts.TypeofNEObject,
             "function": TypeFacts.TypeofNEFunction
         });
-
         const typeofTypesByName = createMapFromTemplate<Type>({
             "string": stringType,
             "number": numberType,
@@ -344,6 +342,7 @@ namespace ts {
             "symbol": esSymbolType,
             "undefined": undefinedType
         });
+        const typeofType = createTypeofType();
 
         let jsxElementType: Type;
         let _jsxNamespace: string;
@@ -1725,6 +1724,10 @@ namespace ts {
             return type;
         }
 
+        function createTypeofType() {
+            return getUnionType(arrayFromMap(typeofEQFacts.keys(), s => getLiteralTypeForText(TypeFlags.StringLiteral, s)));
+        }
+
         // A reserved member name starts with two underscores, but the third character cannot be an underscore
         // or the @ symbol. A third underscore indicates an escaped form of an identifer that started
         // with at least two underscores. The @ character indicates that the name is denoted by a well known ES
@@ -14609,7 +14612,7 @@ namespace ts {
 
         function checkTypeOfExpression(node: TypeOfExpression): Type {
             checkExpression(node.expression);
-            return getUnionType(arrayFromMap(typeofEQFacts.keys(), s => getLiteralTypeForText(TypeFlags.StringLiteral, s)));
+            return typeofType;
         }
 
         function checkVoidExpression(node: VoidExpression): Type {