Auto merge of #1282 - luser:update-gl-generator, r=glennw
Auto merge of #1282 - luser:update-gl-generator, r=glennw

Update gl_generator to 0.5.3 to make generated bindings deterministic.

[I fixed gl_generator](https://github.com/brendanzab/gl-rs/pull/415) to make the bindings it generates deterministic. @jrmuizel had noticed that he was getting a lot of cache misses building with sccache, and this (+ a few sccache fixes) fixes that.

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