test/PCH/headersearch.cpp: Tweak for Windows hosts especially cygming.

This test requires shell feature, to change working directory.
On Windows, current directory cannot be moved nor removed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@127130 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed