Revert "Make sure all temporary files get created under %T."

This reverts commit r244163. The workaround shouldn't be necessary
after r244172, and moreover the commit was slightly buggy as it
dis a simple mkdir without removing the directory first, which could
cause 'File exists' errors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244182 91177308-0d34-0410-b5e6-96231b3b80d8