Put IPCC behind a default-on cargo feature - #113

control: job assigned to worker 01KZPCD9NRED3NTVHRT2P5S19H [factory aws, i-020f6ff49c1d31995] (queued for 55 s)
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task: starting task 0: "setup"
task: process exited: duration 4120 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 15483 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 16 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 997 ms, exit code 0
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task: starting task 4: "build"
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| running 1 test
| test tests::sprockets_example_matches_code_based_generation ... ok
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| test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0. [...]
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|    Doc-tests sprockets_tls
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| running 0 tests
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| test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0. [...]
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|    Doc-tests sprockets_tls_test_utils
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| running 0 tests
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| test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0. [...]
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task: process exited: duration 45258 ms, exit code 0
|W| found 0 output files