Bug 995200 - Enable strict mode for self-hosted code in opt builds, too. r=jorendorff

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extra : rebase_source : bd1ba070396f8556b112dd1dc5b30b3ff5e40fb0
Bug 911147 - Implement Array.prototype.fill. r=jorendorff

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extra : rebase_source : c75210fc3b73a6752f8d9e97c6e376c2f10fbc5c