The test added in r275267 does not work on read-only checkouts because of the use of touch -m -t.

Following Tom Rybka suggestion, the test files are now copied to a temporary directory first.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@275415 91177308-0d34-0410-b5e6-96231b3b80d8