[do not merge] smup

[fitzgen]

Matching PR for servo/mozjs#93

Only has macos64 bindings thus far.

Is it correct to do

$ cargo build
$ ./etc/bindings.sh
$ mv out.rs src/jsapi_macos_64.rs

for the non-DEBUG bindings, and do

$ cargo build --features debugmozjs
$ ./etc/bindings.sh
$ mv out.rs src/jsapi_macos_64_debug.rs

for the DEBUG bindings? (Because that is what I have done here.)

@Ms2ger

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This change is

[Ms2ger]

#291