Bug 961314 - Switch to in-tree mozconfig and new path for JS binary

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extra : rebase_source : f5b3a8435c8c33c2854641c1e0d43a2ef05a3863
Bug 961314 - Switch to using tooltool for gcc and sixgill, r=aki

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extra : rebase_source : b3aa27acefeea114d9ef5157e3ba70a2f2c90887