Auto merge of #11841 - asajeffrey:constellation-logging, r=Manishearth

Send log messages to the constellation

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Send all warnings and errors to the constellation. Warnings are bufferred up, and included in any subsequent error reports. Errors are reported in the same way as panics.

Note that this can't merge yet, as it needs https://github.com/rust-lang-nursery/log/pull/86 to land.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #11776 (github issue number if applicable).
- [X] These changes do not require tests because we don't test crash reporting.

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