tests: Check that we can output to /dev/fd filesystem.

 - An LLVM unique_file() bug could cause us to infinite loop on the later test
   case.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168082 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed