Spurious codegen-units no such file or directory error

[alexcrichton]

http://buildbot.rust-lang.org/builders/auto-linux-musl-64-opt/builds/4608/steps/test/logs/stdio
https://gist.github.com/alexcrichton/3aa10bbb13acd11fc236af2eb31cd4d8

failures:

---- [codegen-units] codegen-units/partitioning/local-drop-glue.rs stdout ----

error: compilation failed!
status: exit code: 101
command: x86_64-unknown-linux-gnu/stage2/bin/rustc /buildslave/rust-buildbot/slave/auto-linux-musl-64-opt/build/src/test/codegen-units/partitioning/local-drop-glue.rs -L x86_64-unknown-linux-gnu/test/codegen-units/ --target=x86_64-unknown-linux-musl -L x86_64-unknown-linux-gnu/test/codegen-units/partitioning/local-drop-glue.stage2-x86_64-unknown-linux-musl.codegen-units.libaux -C prefer-dynamic -o x86_64-unknown-linux-gnu/test/codegen-units/partitioning/local-drop-glue.stage2-x86_64-unknown-linux-musl -C linker=/musl-x86_64/bin/musl-gcc -C ar=ar --cfg rtopt -C rpath -O -L x86_64-unknown-linux-musl/rt -Zprint-trans-items=lazy -Zincremental=tmp/partitioning-tests/local-drop-glue
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
error: could not create the directory `tmp/partitioning-tests/local-drop-glue`: No such file or directory (os error 2)
error: aborting due to previous error

------------------------------------------

thread '[codegen-units] codegen-units/partitioning/local-drop-glue.rs' panicked at 'explicit panic', /buildslave/rust-buildbot/slave/auto-linux-musl-64-opt/build/src/tools/compiletest/src/runtest.rs:2239
note: Run with `RUST_BACKTRACE=1` for a backtrace.


failures:
    [codegen-units] codegen-units/partitioning/local-drop-glue.rs

test result: FAILED. 33 passed; 1 failed; 0 ignored; 0 measured

cc @michaelwoerister, thoughts?

[alexcrichton]

I haven't seen this in a long time, so I will presume fixed.

[michaelwoerister]

🎉