Bug 883691 - Fix some simple clang warnings in SpiderMonkey.  r=bhackett.

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extra : rebase_source : 168fe0710a42ebf3f90c14ecb12de32305987586
Bug 881579 - Use the canonical #ifndef wrapper form in SpiderMonkey headers so that GCC and clang can avoid including them more than once per compilation unit.  r=benjamin.

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extra : rebase_source : f9d2b33defe07837da4828a57c66fe0ea6772bae