Auto merge of #47106 - EdSchouten:compiletest-cloudabi, r=alexcrichton

Tiny fixes to make compiletest work for CloudABI cross builds

I'm currently working toward getting a `src/ci/docker` container working to do isolated/automated builds and testing of `x86_64-unknown-cloudabi`. This is working pretty well, but still requires some fixes to `libtest` and `compiletest`. Here is the first set of fixes that I had to apply.