Fall back to /dev/urandom on EPERM for getrandom

[tbu-]

This can happen because of seccomp or some VMs.

Fixes #52609.

[rust-highfive]

r? @TimNN

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[Mark-Simulacrum]

r? @alexcrichton

[sfackler]

@bors r+

[bors]

📌 Commit bd8885d has been approved by sfackler

[bors]

⌛ Testing commit bd8885d with merge ec15eabae9f80168e44f5e7a0f9f275bd8448209...

[bors]

💔 Test failed - checks-travis

[rust-highfive]

The job arm-android of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[01:54:31] test string::test_split_off_mid_char ... ok
[01:54:31] test string::test_str_truncate ... ok
[01:54:31] test string::test_str_truncate_split_codepoint ... ok
[01:54:31] test string::test_str_truncate_invalid_len ... ok
[01:54:31] died due to signal 11
[01:54:31] 
[01:54:31] 
[01:54:31] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "arm-linux-androideabi" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--"
[01:54:31] expected success, got: exit code: 3
---
travis_time:end:1c4b4b4a:start=1558284376383697698,finish=1558284376392250098,duration=8552400
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:145006f2
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:09c54b24
travis_time:start:09c54b24
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:06c2fde3
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[alexcrichton]

@bors: retry