rmdir of non-empty directory

[wsmoses]

I think probably related to previous issues, but when gg tries to remove the temporary directory created (presumably in https://github.com/StanfordSNR/gg/blob/cbb81f98325957f1d9d873fae296d371e950ca97/src/util/temp_dir.cc#L30) there's still temporaries left in the directory in an error condition.

[artemdinaburg]

I was about to file this same issue; I ran into this when failing to build LLVM's opt, which sounds exactly like what the original submitter was trying to do :).