Assert emitting declarations for a global exported using an export specifier

[mhegazy]

Reported by @mprobst in #3514

mimial repro:

a.d.ts:

declare class X {}

b.ts:

/// <reference path="a.d.ts"/>
export {X};
export function f () {
    var x: X;
    return x;
}

tsc --d b.ts

Debug Failure. False expression: isDeclarationVisible unknown: SyntaxKind: 218
at Object.assert (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:1418:23)
at Object.fail (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:1423:19)
at determineIfDeclarationIsVisible (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:12614:34)
at isDeclarationVisible (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:12620:41)
at getIsDeclarationVisible (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:11969:22)
at /Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:11964:82
at Object.forEach (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:748:30)
at hasVisibleDeclarations (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:11964:20)
at Object.isSymbolAccessible (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:11904:57)
at Object.trackSymbol (/Users/martinprobst/src/angular/node_modules/typescript/bin/typescript.js:23053:53)