DeclarationDir needs to be handled in excludeSpecs if exclude is not specified

[sheetalkamat]

TypeScript Version: 2.9.0-dev.201xxxxx

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Code
Should declarationDir also be part of excludeSpec if exclude is not specifies in the tsconfig just like outDir?

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.

Expected behavior:

Actual behavior:

Playground Link:

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[a-tarasyuk]

@mhegazy @sheetalkamat I'll work on this issue if you don't mind

[mhegazy]

go for it.